Arecipe 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?

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