A sports car going at an average speed of 108 km/h takes 15 minutes to complete a lap on a racing track. How much speed (in km/h) should be increased to complete the lap in 9 minutes?

A sports car going at an average speed of 108 km/h takes 15 minutes to complete a lap on a racing track.

Length of racing track = $$108\times\ \frac{15}{60}$$ (Here 15 is divided by 60 to convert the minutes into hours.)

= $$108\times\ \frac{1}{4}$$

= 27 km

Speed when the one lap on a racing track completed in 9 minutes = $$\frac{27}{\frac{9}{60}}$$

= $$\frac{27\times\ 60}{9}$$

= $$3\times60$$

= 180 km/h

Increase in the speed = (180-108) km/h

= 72 km/h