Donald has a coin collection. he has 36 dimes, 72 quarters, and 18 nickels. he wants to arrange them into equal groups with only one type of coin in each group. how many can he put in each group?
a. 1
b. 2
c. 3
d. 4 e. 9 f. 12

The way I understand the question is that he wants to have for example many groups of 2, many groups of 3, etc, etc.

There are many possibilities, so let's just look at all the options!

a. 1
 - it's technically possible, as 36, 72 and 18 are each divisible by 1 (but I don't think it's a "group"
 
b. 2
 - yes, this is possible!  36, 72 and 18 are each divisible by 2 (they're all even)

c. 3
 yes, he can have piles of 3 as 36, 72 and 18 are each divisible by 3
d. 4
NO! they're not divisible by 4

E. 9
yes! it would be 2 piles of nickels, 4 of quarters and 8 of dimes

F. 12
NO! they're not divisible by 12