Division By Zero Error In Laravel Web App

I am not a programmer, and I'm trying to fix an error I'm getting in a web app I had developed recently.

It's basically a project management app, and we are importing keyword rankings from ahrefs. Then we run some calculations to compare with previous months and years.

In researching the division by zero error, I understand this is more less a math problem and we are trying to divide zero by zero or something. But it's all chinese to me. So I'm hoping someone would be kind enough to spare a few minutes and help me fix whatever syntax in wrong in the function below?

This is from the app/helpers.php file inside my laravel app.

If it helps, when I have debug on, it tells me this specific line is causing the error:

$percentage = $difference/$previous_month*100;

Thanks in advance and orig full code for function is below

function getKeywordData($website)
    {
		if($website->lastMonthTop10Keywords)
		{
			$last_month = $website->lastMonthTop10Keywords->top3 + $website->lastMonthTop10Keywords->top4_10;
			$previous_month = $website->previousMonthTop10Keywords->top3 + $website->previousMonthTop10Keywords->top4_10;
		}
		else
		{
			$last_month = 0;
			$previous_month = 0;
		}
	
		$rankingData['last_month'] = $last_month;
		$rankingData['value'] = '0';
		$rankingData['arrow'] = 'down';
		$rankingData['bootstrap'] = 'danger';

		if($last_month >= $previous_month) {
			$rankingData['arrow'] = "up";
			$rankingData['bootstrap'] ="success";
			$difference = $last_month - $previous_month;
			$percentage = 0;
			if($difference > 0)
			{
				$percentage = $difference/$previous_month*100;
			}
			
		}
		else
		{
			$difference = $last_month - $previous_month;
			$percentage = $difference/$previous_month*100;
		}

		$rankingData['value'] = round($percentage, 2);
		return $rankingData;
    }

Unfortunately I am not a programmer, so I haven't tried any of the solutions already provided in similar questions about division by zero errors. It's not lack of effort or that I'm lazy. I'm just not versed enough in coding to be able to apply a fix unless the code is verbatim to my function, and I can simply cut n paste back into the file. I only understand css code.

$percentage = $difference / $previous_month * 100;

I assume it may occur that "there is no previous month", in which case we refer to it as "the first month". In this case, the value of the "previous month" is 0, and division by 0 is not possible. Therefore, we need to check whether the value of the "previous month" is 0 or not. If it is 0, we do not perform the division.If it is not 0, then we proceed with the division.

$percentage = $previous_month === 0 ? 0 : $difference / $previous_month * 100;

In PHP, there is an option to write a short if-else syntax as follows: "condition - true or false result" ? "what happens if true" : "what happens if false". In my case, I set the condition to check if the value of the previous month is 0. After the "?", I wrote 0 fixedly because I assume that in this case, the percentage value will be 0%. However, you can modify this value to anything you desire. After the ":", I included the original formula, as in that case, the value of the previous month is definitely not 0.