Set up a fraction with 2 cups of sugar (s) at the top and 32 brownies (b) at the bottom. 2s/32b. Now, set up the next fraction with x cups of sugar (because we don't know the amount of sugar) at the top and 72 brownies (b) at the bottom. Set them equal. Your equation should be 2s/32b=x/72b. Cross multiply these values (if you wrote them down; 32x=144) and solve for x.