It has no solution
18m+7=18m+7
Which means they are the same equation !!
Well she has $10 and each spinach is $3 so she can not but no more than 3.
Simply present that you would split them up as a factor of two. ( make two lines going either vertically or horizontally. place in varriations, a marble in one line and a marble in the other and then count the leftover
(2, 8) because 8 is not negative
hope it helps,
xXbeautyXx