Problem

During the first 18 min of a 60 min trip, a car has an average speed of

11 \text{ ms}^{-1}

. What should be the average speed for remaining 42 min so that car is having an average speed of

21 \text{ ms}^{-1}

for the entire trip? a.

25.3 \text{ ms}^{-1}

29.2 \text{ ms}^{-1}

31 \text{ ms}^{-1}

35.6 \text{ ms}^{-1}