Maybe it’s 3 but it actually depends on the equation . . .
Answer:

Step-by-step explanation:
Given

Required
Determine the expression for s
The speed is calculated as:

Substitute S for speed

Let the number of books be b and the time be m.
The expression becomes

Hence, the expression for the scenario is:

90 square ft (try and look at it like each side is a 2d rectangle, find the areas of the sides and then add them up.)
Answer:
the pic is black send another one