let annual installment be 100. Now shortcuts is to add rate of interest in 100 for time (i,e. 3 installments).
means 100 , 112 & 124
now shortcuts is( total debt = add these 3 values = 100 + 112+124 = 336 )
Now take ratio of annual installment / total debt = 100 / 336 = X/ 1092
{let actual installment be X)}
so X = 100 *1092/336 = 325
So annual payment that will discharge a debt of Rs. 192 due in 3 years at 12% SI = Rs.325 ans