Let x = part of the $50,000 that is to be invested for 15 percent per year.

So, 50,000 -x = the part to be invested for 7 percent per year.

Interest = principal * rate

x(0.15) +(50,000 -x)(0.07) = 6000

0.15x +3500 -0.07x = 6000

0.15x -0.07x = 6000 -3500

0.08x = 2500

x = 2500/0.08

x = 31,250 dollars.

Hence, 50,000 -x = 50,000 -31,250 = 18,750 dollars.

Therefore, to earn $6000 in interest per year, $31,250 should be invested for 15 percent per year, and $18,750 for 7 percent per year. -------answer.