System Applications word problem that has me confused.

Question

Last year Ms. Díaz invested $9,000. Some of her money was invested in stocks paying 6% annually and the rest was invested in bonds paying 7.5% annually. She received a total of $600 from these investments for the year. How much did she invest in the stocks paying 6%?

Answer 1

x represents the amount invested at 7.5%

9000 - x represents the amount invested at 6%

0.075x + 0.06(9000 - x) = 600

Can you solve for x and answer?