3/12+25/30;10/24-21/54;30/54+22/30;28/40-10/75

1) 3/12+25/30=(3*5+25*2)/60=65/60=1 1/12

2) 10/24-21/54=(10*2,25-21)/54=15/540=3/108

3) 30/54+22/30+(30+22*1,5)/54=63/54=1 9/54=1 1/6

4) 28/40-10/75=(28*1,875-10)/75=425/750=17/30