Exercise 40 Page 42

We will begin with finding the area of the base. We see that the base is a square since it is a rectangle with equal sides. To find its area, we will use the formula for the area of a square, where $b$ is the side length. The four other sides are also identical — each is a rectangle with a length $\ell$ and a width $b.$ The formula for the area of a rectangle tells us that the area of a rectangle is the length multiplied by the width. In our case, these lengths are $\ell$ and $b,$ respectively. We can now add add these expressions to write the formula for the surface area $S$ of the prism. Keep in mind there are $2$ bases and $4$ sides.