3)2 1/7- (9/28 - 3/14)=
4)1 2/9- (1 5/27 - 13/18)=

1)    ...........=3 1/7 -19/21+1/14=3 6/42 - 38/42+3/42=2 13/422)   ...........=2 4/9 - 1 5/6+11/12=2 16/36 - 1 30/36+33/36=2 19/363)   ..........=2 1/7 - 9/28+3/14=2 4/28 - 9/28+6/28=2 1/284)   ...........=1 2/9 - 1 5/27+13/18=1 12/54 - 1 10/54+39/54=41/54