#### Answer

8$\frac{1}{4}$ hour

#### Work Step by Step

Given four tires of a car can be replaced in $\frac{3}{4}$ hour
Therefore we need to find how much time it will take to replace tires of 11 cars = 11 $\times$ $\frac{3}{4}$
= $\frac{33}{4}$
=8$\frac{1}{4}$ hour