One day, 90 students were travelling in a bus and the ratio of the number of boys to that of girls was 2 : 1. The next day,
the number of students remained the same, but the ratio of the number of boys to that of girls became 3 : 2. What was
the difference between the numbers of boys travelling in the bus on both days ?

A

18

B

6

C

14

D

30