#### Answer

$\frac{3}{4}$

#### Work Step by Step

To simplify a ratio, we divide by a fraction that is equal to $1$ (a fraction with the same number in the numerator and denominator is equal to $1$). In this case, we use $\frac{15}{15}$: $$\frac{45}{60}\div\frac{15}{15}=\frac{3}{4}$$