Answer:
C :7 : 5
Explanation:
Girls - 42 : 72
boys - 30 : 72
You solve this by finding the greatest common factor of 42 and 30.
The greatest common factor happens to be 6.
So, since the unreduced ratio is 42 : 30, the reduced ratio will be 42/6 : 30/6, which is 7 : 5