A recipe called for using 5 1/8 cups of cups of flour before baking and another 8 7/9 cups after baking. What is the total amount of flour needed in the recipe?

It'll be 13 65/72 and you have to simplify it

First convert the mixed numbers to improper fractions ...

rule: a b/c = (ac+b) / c

41/8+79/9

Now to add/subtract fractions you need a common denominator (preferably the least common multiple)

(41/8) (9/9) + (79/9) (8/8)

369/72+632/72

(369+632) / 72

1001/72 now back to a mixed number ...

(936+65) / 72

13 65/72