Answer:
Step-by-step explanation:
Let x represent the amount invested at 9%. Then 6000-x is the amount invested at 7%, and the total interest earned is ...
0.09x + 0.07(6000-x) = 510
0.02x + 420 = 510 . . . simplify
0.02x = 90 . . . . . . . . . subtract 420; next, divide by 0.02
x = 4500 . . . . . . . . . . . the amount invested at 9%
6000-x = 1500 . . . . . .the amount invested at 7%
$4500 was invested at 9%; $1500 was invested at 7%.