WBJEE 2015 Math Solved Paper

A person goes to office by a car or scooter or bus or train, probability of which are 1/7, 3/7, 2/7 and 1/7 respectively.Probability that he reaches office late, if he takes car, scooter, bus or train is 2/9, 1/9, 4/9, and 1/9 respectively. Giventhat he reached office in time, the probability that he travelled by a car is