so she put in 3 and 1/9 or 9/9+9/9+9/9+1/9 or 28/9
28/9+x=13/4 13/4-28/9=x
so we convert so that the bottom numbers are the same
a short cut is 3 and 1/4+x=3 and 1/9 3 1/9+x=3 1/4 subtract 3 from both sides 1/9+x=1/4 subtract 1/4 from both sides x=1/4-1/9 convert bottom number to same thing 1/9=4/36 1/4=9/36 x=9/36-4/36 x=5/36 5/36 cups
