a sum of 390200 is to be paid back in 3 equal annual installments how much is each installments if rate is 4% per annum compounded annually

Why cant we do this in this manner?

Let the principal 390200 be divided into 3 sums say P, Q R such that P+Q+R = 390200

Let an instalment of Rs I be paid after 1 year to clear a principal of P therefore

P*104 / 100 = I

Let an instalment of Rs I be paid after 2 years to clear a principal of Q therefore

Q * 104 * 104 /10000 = I

Let an instalment of Rs I be paid after 3 years to clear a principal of R therefore

R* 104 *104 *104 / 1000000 = I

so I *100/104 = P

I * 10000 /10816 = Q

I * 1000000 /1124864 = R so {(100 /104) + (10000 /10816) + (1000000 /1124864)} I = P+Q+R = 390200.

{(1081600 + 1040000 + 1000000 ) / 1124864 } I = 390200

(3121600 /1124864 )I = 390200

I = 1124864/8 = 140608