#### Explanation:

The formula for calculating the change between two values is:

$p = \frac{N - O}{O} \cdot 100$ where $p$ is the percent change, $N$ is the New Value and $O$ is the Old Value. In this problem we are give $p$ (-60 - the suit was discount which means the change was negative_ and $N$ ($648). We can substitute these into the formula and solve for $O$: $- 60 = \frac{648 - O}{O} \cdot 100$$- \frac{60}{100} = \frac{648 - O}{O} \cdot \frac{100}{100}$$- 0.6 = \frac{648 - O}{O} \cdot 1$$- 0.6 = \frac{648 - O}{O}$$O \cdot - 0.6 = O \cdot \frac{648 - O}{O}$$O \cdot - 0.6 = \cancel{O} \cdot \frac{648 - O}{\cancel{O}}$$- 0.6 O = 648 - O$$- 0.6 O + O = 648 - O + O$$\left(1 - 0.6\right) O = 648$$0.4 O = 648$$\frac{0.4 O}{0.4} = \frac{648}{0.4}$$O = 1620\$