They would have b^2 + 3b. Solution?
B*2 = b^2
b + b = 2b
2b + b = 3b

= b^2 + 3b

B*2 is not equivalent to b^2.
Sorry, I just forgot about it because; if it's b*b, that's b^2. If it's 2*b, that's what you're talking about. So, the answer would be your answer: 5b.
Let B be the number of books Bob has.

Since it is said that Jake has twice the number of books Bob has, we can say that Jake has a number of books given by 2B.

Pete has B more books than Bob has, which can be said as B+B, which is also 2B.

For simplicity:
B=Bob books
2B=Jake books
2B=Pete books

Therefore, if we add Bob's, Jake's and Pete's books, we get:

Hope that helps.