First, look at all of the answers.
It cannot be A because 3 does not go into 28 or 35.
It cannot be B because 9 and 15 both do not go into 28 or 35.
It cannot be C because 9 does not go into 28 or 35.
Even though the only answer left is D, let's just double check. 28 divided by 7 is 4, and 35 divided by 7 is 5. 28:35=4:5. The answer is D.
Hope it helped! :)
