A and B start to walk from point P towards point Q. The distance between P and Q is 9 km. B starts 4 minutes after A. A, on reaching Q, immediately returns and after walking a kilometre meets B. If A’s speed is a kilometre in 10 minutes, what is B’s speed in kilometres per minute?

Correct option is C

A's speed = 1 km per 10 min Time taken by A to reach Q = 9 × 10 = 90 min B starts 4 minutes later, so he has walked for 90 – 4 = 86 min when A reaches Q .
A walks 1 km back ( 10 min ), meaning B has walked for 96 min . B covers 8 km in 96 min , so speed is: Speed of B = 8/96 = 1/12 km/min