$77,700 at 10%, $62,000 at 18%
Let's assign the variable s for the amount of money that will be put into the safe investment. That means that 139700-s will the amount invested in the risky investment. So we can create the equation
0.10s + 0.18(139700 - s) = 18930
Now solve for s
0.10s + 0.18(139700 - s) = 18930
0.10s + 25146 - 0.18s = 18930
6216 - 0.08s = 0
6216 = 0.08s
77700 = s
So she should invest $77,700 in the safe investment at 10% and ($139,700 - $77,700) = $62,000 in the risky investment at 18%