Steps:
1. Sugar needed to make cake is and Sugar needed for frosting is
2. Total number of cups of sugar needed is
3. As we are having different denominators,
4. We have to take LCD, by listing multiples of denominators as shown
Then, LCD is
5. As the denominator is changed, then the numerator also to be changed by the same number, then
6. Now the denominators are common, and then add numerators
7. Therefore, the fraction is
Hence, the sum of the fraction is.