SELECT a.assembly_name,
	a.financial_year,
	a.total_expenditure,
	SUM(b.ac_bill_amount) AS TOTAL_AC_BILL
	FROM fund_allotment AS a INNER JOIN mla_ac_bill AS b
	ON a.assembly_name = b.assembly_name and a.financial_year = b.financial_year
	GROUP BY a.assembly_name,a.financial_year,a.total_expenditure

var result = fundAllotment
    .Join(mlaAcBill,
        a => new { a.AssemblyName, a.FinancialYear },
        b => new { b.AssemblyName, b.FinancialYear },
        (a, b) => new
        {
            a.AssemblyName,
            a.FinancialYear,
            a.TotalExpenditure,
            b.AC_Bill_Amount
        })
    .GroupBy(x => new
    {
        x.AssemblyName,
        x.FinancialYear,
        x.TotalExpenditure
    })
    .Select(g => new
    {
        g.Key.AssemblyName,
        g.Key.FinancialYear,
        g.Key.TotalExpenditure,
        TotalACBill = g.Sum(x => x.AC_Bill_Amount)
    });

from fa in fund_allotment
join mab in mla_ac_bill
	on new { fa.assembly_name, fa.financial_year }
	equals new { mab.assembly_name, mab.financial_year }
group mab.ac_bill_amount
	by new { fa.assembly_name, fa.financial_year, fa.total_expenditure }
	into g
select new
{
	g.Key.assembly_name,
	g.Key.financial_year,
	g.Key.total_expenditure,
	TOTAL_AC_BILL = g.Sum()
};