Jupiter's average is 778km away from the sun and Mars is 550 less kilometers away from the sun than Jupiter. So you just subtract 778 to 550 which equals to 228. Therefore the average distance Mars is 228km away from the Sun
Each book costs 3 dollars and b is the number of books borrowed that one month. In that month, she also needs to pay 16 dollars for her membership so if you put all of it together, you get 3b + 16.