Exercise 1 Page 357

When adding or subtracting fractions, they should have the same denominator. In this exercise, we have two fractions with different denominators. Since $15$ is a multiple of $5$ and $3,$ we can multiply both the numerator and denominator of $\frac{3}{5}$ by $3$ and $\frac{2}{3}$ by $5$ to create a common denominator.