Sherrie travels 120 miles in 3 hours. Find the unit rate of speed by filling in the missing number.

$\displaystyle\frac{{{120}\ \text{ miles}}}{{{3}\ \text{ hours}}}=\frac{{?\ \text{ miles}}}{{{1}\ \text{ hour}}}=?\frac{{\text{miles}}}{{\text{hour}}}\usepackage{cmbright}\Huge\$