First for 7 we need to find out how many ninths are in a third and there are 3/9 in a third so now we multiply 3/9 by 2 which is 6/9 now we subtract 7/9-6/9 which is 1/9 so 1/9 is left. (Iff I'm wrong sorry I did this is like a minute.)
Add 7 to both sides.
13+7=
20
C is the answer. Hope that helps C:lol
