1) 3 15/28 + 6 22/35
First, convert both mixed numbers to improper fractions:
3 15/28 = (328 + 15)/28 = 89/28
6 22/35 = (635 + 22)/35 = 217/35

Now, add the fractions:
89/28 + 217/35
= (8935 + 21728)/(28*35)
= (3115 + 6076)/980
= 9191/980

Convert the result back to a mixed number:
9191 ÷ 980 = 9 r11, so the answer is 9 11/980

2) 4.25 + 1 11/12 - 7/15
Convert the mixed number to an improper fraction:
1 11/12 = (1*12 + 11)/12 = 23/12

Now, add the fractions:
4.25 + 23/12 - 7/15
= 17/4 + 23/12 - 7/15
= 255/60 + 115/60 - 28/60
= 342/60
= 57/10
= 5.7

3) 7 7/30 - (3 2/15 - 1 5/12)
First, subtract the mixed numbers in the parentheses:
3 2/15 - 1 5/12
= 47/15 - 17/12
= (474 - 175)/(15*4)
= (188 - 85)/60
= 103/60

Now, subtract this result from the whole number:
7 7/30 - 103/60
= 217/30 - 103/60
= 434/60 - 103/60
= 331/60
= 5 31/60