The diameter of a wheel of a bus is 90 cm which makes 315

We have to calculate the speed of the bus. The wheel makes 315 revolutions per minute. We have,

Diameter of the wheel $(d)=90 \mathrm{~cm}$

So distance travelled in one revolution,

$=\pi d$

$=\frac{22}{7}(90) \mathrm{cm}$

$=\frac{1980}{7} \mathrm{~cm}$

So,

Speed $=$ (Distance travelled in one revolution) (Number of revolution per minute)

So,

Speed $=\left(\frac{1980}{7}\right)(315) \mathrm{cm} / \mathrm{min}$

$=89100 \mathrm{~cm} / \mathrm{min}$

Convert the unit of speed as,

$89100 \mathrm{~cm} / \mathrm{min}=\frac{89100(60)}{100000}$

$=53.46 \mathrm{~km} / \mathrm{hr}$