To solve the given expressions:

3/12 + 25/30
= (3/12) + (25/30)
= (1/4) + (5/6)
= (1/4)(3/3) + (5/6)(2/2)
= 3/12 + 10/12
= 13/12

10/24 - 21/54
= (10/24) - (21/54)
= (5/12) - (7/18)
= (5/12)(3/3) - (7/18)(2/2)
= 15/36 - 14/36
= 1/36

30/54 + 22/30
= (30/54) + (22/30)
= (5/9) + (11/15)
= (5/9)(5/5) + (11/15)(3/3)
= 25/45 + 33/45
= 58/45

28/40 - 10/75
= (28/40) - (10/75)
= (7/10) - (2/15)
= (7/10)(3/3) - (2/15)(2/2)
= 21/30 - 4/30
= 17/30

Therefore, the solutions to the given expressions are: