A:amount of money invested in the account with 3% simple interest
B: amount of money invested in the account with 4.5% simple interest
a+b=25000 ——>a=25000-b
0.03a+0.045b=900
30a+45b=900000
2a+3b=60000
2(25000-b)+3b=60000
50000-2b+3b=60000
B=10000
A=25000-10000=15000