If someone invests $8000 at 7%, how much additional money must he invest at 4% so that his total annual income may equal 5% of his entire investment?
.07(8000) + .04x = .05(8000+x)
times 100
7(8000) + 4x = 5(8000+x)
56000 + 4x = 40000+5x
-x = -16000
x = 16000