Question

a man borrowed $85,000 of wich he pays a part of at 9% interest and the rest at 12% if his total interest payment is $9300 per year how much did he borrow at each rate of interest ?

Answer 1

Let X = the amount borrowed at 9% interest
let Y = the amount borrowed at 12% interest.

Here is what you know:
X + Y = 85,000
0.09 X + 0.12 Y = 9,300

Now solve those two simultaneous equations. One easy way is to multiply both sides of the first equation by 0.09.
0.09 X+ 0.09 Y = 7,650
Now subtract that from the second equation to eliminate the X variable.
0.03 Y = 1650
Y = 55,000
X = 30,000