How do I solve this problem?

Question

A total of $16,000 is invested in two corporate bonds that pay 3.5% and 5% simple interest. The investors want an annual interest income of $650 from the investments. What amount should be invested at 3.5% bond?

Answer 1

a + b = 16000 -----> b = 16000 - a

0.035a + 0.05b = 650

0.035a + 0.05(16000 - a) = 650

0.035a + 800 - 0.05a = 650

-0.015a = - 150

a = $10,000