You can
put this solution on YOUR website!Your calculations are correct.
The amount invested at 7% is $9000
The amount invested at 5% is $4500.
This statement is wrong : .05(13,500 - 9000)=4500
It should be 0.05*(13500-9000) = 225
If that is the reason your instructor is rejecting your answer, I feel for you. It will be a really long year in a classroom with a nit picker like that :(