(4:2 1/5)-(1/7+1/14)

(4:21/5)-(1/7+1/14)
(4×5/21=20/21)-(1/7+1/14)
20/21-(2/14-7/14=-5/14)
20/21-/(-5/14) = 40/42-(-15/42)
                       =40/42+15/42
                       =55/42