Arecipe calls for a total of 3 2/3 cup flour and sugar. if the recipe calls for 1/4 cups of sugar, how much flour does he need

You'll want to convert 3 2/3 into a common denominator with 1/4.
The nearest common denominator of 3 and 4 is 12. 
1/4 * 3/3 = 3/12
2/3 * 4/4 = 8/12
You need 3 and 8/12 in total so subtract 3/12 from 3 8/12 to get the flour
3 8/12 - 3/12 = 3 5/12.
You would need 3 5/12 cups of flour.

5\16 x 2\5 = 10/80simplify to 1/80