4) (7/8-13/20) + 9/10
9/40 + 9/10
9/8
5) ( 7/18 - 1/12 ) + 5/6
11/36 + 5/6
41/36
6) ( 3/4 - 8/15 ) - 17/20
13/60 + 17/20
16/15
