Here's the image for the question I have:

C::10:15

Step-by-step explanation:

It is C because he had 15 hours of first aid and 10 hours of cpr and the question says CPR TO FIRST AID therefore the number of CPR training hours will come before the number of First Aid training hours. If it would have asked you to reduce the ratio it would have been 2:3 because you would have had to divide both sides by 5 resulting in the smallest possible ratio.

HOPE THIS HELPS YOU OUT!