Let
x ------> money invested in stocks
y ------> money invested in bonds
z -----> money invested in CDs
we have that
x+y+z=210,000 -------> equation A
y=z+15,000 ------> equation B
Remember that
the formula of simple interest is equal to
I=P(rt)
In this problem
I1=8.6%=0.086
I2=3.7%=0.037
I3=6%=0.06
so
0.086x+0.037y+0.06z=12,450 ---------> equation C
we have the system of equations
x+y+z=210,000 -------> equation A
y=z+15,000 ------> equation B
0.086x+0.037y+0.06z=12,450 ---------> equation C
using a calculator
we have that
(please wait a minute to calculate the system)
x=65,000
y=80,000
z=65,000
therefore
the answer is
money invested in stocks was $65,000
money invested in bonds was % 80,000
money invested in CDs was $ 65,00