## Elementary Algebra

According to the question, 20 percent of a certain number is 15. Therefore, we denote the unknown number with $x$ in order to write the following equation: Step 1: $\frac{20}{100}\times x=15$ Step 2: $20x=100\times15$ Step 3: $20x=1500$ Step 4: $x=\frac{1500}{20}$ Step 5: $x=75$ Therefore, $20$% of $75$ is $15$.