Final answer:
The amount invested at 7% was $3000, the amount invested at 9% was $3800, and the amount invested at 12% was $7000.
Step-by-step explanation:
Let's denote the amount invested at 7% as x, the amount invested at 9% as y, and the amount invested at 12% as x + y + 700.
We can set up the following system of equations based on the given information:
= 7500 (Total amount invested)
- x(0.07) + y(0.09) + (x + y + 700)(0.12)
= 772 (Total annual income)
Simplifying and solving this system of equations, we can find that :
x = 3000, y = 3800, and x + y + 700 = 7500.
Therefore, $3000 was invested at 7%, $3800 was invested at 9%, and $7000 was invested at 12%.