Question 1130662
Martha invested some money at 12%, this is 0.12M 
That money is part of the 8,000 joint investment.
Peter invested what's left at 6%, this is 0.06(8,000 - M)
.
0.12M + 0.06(8,000 - M) = 570
0.12M + 480 - 0.06M = 570
0.06M = 90
M = 1,500
Martha invested $1,500