Suppose a rectangle has length 5 cm and width 2 cm. What is the area of the rectangle?
We use the formula A = lw, substituting 5 for l and 2 for w, to find that
A = (5)(2) = 10 cm2
Sometimes these problems are a little more interesting. See how we said "interesting" instead of "complicated?" Man, are we good. Instead of getting the answer immediately, substituting in numbers may leave us with an equation in one variable that needs to be solved to find the answer.