I think the answer is b i've never learned this sorry :(
I really need one too. Thanks for the question.
Mandy Increases her books by 2 per month.
Bill increases his books by 4 per month.
Month Mandy Bill
May 18 4
June 20 8
July 22 12
August 24 16
Sept 26 20
Oct 28 24
Nov 30 28
Dec 32 32
At the end of December they will have read the same amount of books.
Let's first denote:
F - a favorable response
F' - an unfavorable response
S - successful
We know that:

So, from the conditional probability, we can calculate:

Answer E.