brian earned $14,000 last spring giving swimming lessons. He invested part of the money at 5% simple interest & the rest at 3%. In one year, he earned a total of $570 interest. How much did he invest at each rate?

A = 7500

B = 6500

Explanation:

we buid the equation:

A + B = 14,000

then: B = 14,000 - A

interest formula:

A x (0.05 x 1) + (14,000-A) x (0.03 x 1) = 570

(0.05A - 0.03) A + 420 = 570

A = (570 - 420) / 0.02

A = 7,500

B = 14,000 - A = 14,000 - 7,500 = 6,500