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

Let usual speed = v km/h. Time at usual speed for 150 km = 150/v hours. Time at (v-10) km/h = 150/(v-10) hours. Given: 150/(v-10) - 150/v = 0.5 (30 minutes = 0.5 hours). Solving: 150v - 150(v-10) = 0.5v(v-10), so 1500 = 0.5(v² - 10v), giving v² - 10v - 3000 = 0, or (v - 60)(v + 50) = 0. Thus v = 60 km/h (positive). For 90 km at (v-15) = 45 km/h: time = 90/45 = 2 hours.