Chapter 4 - Proportions, Percents, and Solving Inequalities - 4.1 - Ratios and Proportions - Problem Set 4.1 - Page 149: 58

The width of the rectangle is 36 centimeters.

Let w represent the width of the rectangle. The ratio of the width to its length is $\frac{4}{5}$, and the length is 45 centimeters. We set up the following proportion: $\frac{4}{5}$ = $\frac{w}{45}$ We cross multiply to obtain: 4 $\times$ 45 = 5 $\times$ w 180 = 5w Divide both sides by 5. w = 36. The width of the rectangle is 36 centimeters.