Akhil takes 30 minutes extra to cover a distance of $150 \mathrm{~km}$ if he drives $10 \mathrm{~km} / \mathrm{h}$ slower than his usual speed. How much time will he take to drive $90 \mathrm{~km}$ if he drives $15 \mathrm{~km}$ per hour slower than his usual speed?

2 h

Let usual speed = x km/h

According to question ,

\(\frac{150}{x - 10}\) - \(\frac{150}{x}\) = \(\frac{30}{60}\)

\(\frac{150x - (x-10)150}{x(x - 10)}\)= \(\frac{1}{2}\)

On solving ,

x = 60 km/h

So speed at which Akhil drove 90 km = 60 - 15 = 45 km/h

Time taken to cover 90km = \(\frac{90}{45}\) = 2 hours