//{formula`SUM(C${i}:D${i})`} it can we written as this.
let data = [{
        department : 'CSE', student_details : [{
            student_name : 'A 1', roll_number : 1, marks_1 : 80, marks_2 : 70, marks_total : {formula : `SUM(C2:D2)`}
        },
        {
            student_name : 'B 1', roll_number : 2, marks_1 : 99, marks_2 : 90, marks_total : {formula : `SUM(C3:D3)`}
        }]
    },
    {
        department : 'ME', student_details : [{
            student_name : 'A 2', roll_number : 1, marks_1 : 78, marks_2 : 87, marks_total : {formula : `SUM(C2:D2)`}
        },
        {
            student_name : 'B 2', roll_number : 1, marks_1 : 79, marks_2 : 89, marks_total : {formula : `SUM(C3:D3)`}
        }]
    }];