Hi there:)
Let's translate this question into numerical data
First find the interest for two years
15,000×0.085×2=2,550
Now exclude 4000 from the amount invested 15000-4000=11000
(CD's penalty for withdrawal is 4,000×0.085×(6÷12)=170)
After that find the interest for the rest of the time
11,000×0.085×7=6,545
how much money did Rachel have when the CD reached maturity, not including the amount she withdrew
11,000+2,550−170+6,545=19,925
Hope it helps