To solve each of the given equations:

1) 3/9 = b/12
Cross multiply to solve for b:
9b = 3(12)
9b = 36
b = 36/9
b = 4

2) b/5 = 6/15
Cross multiply to solve for b:
15b = 5(6)
15b = 30
b = 30/15
b = 2

3) 2/9 = 8/b
Cross multiply to solve for b:
2b = 9(8)
2b = 72
b = 72/2
b = 36

4) 10/b = 30/33
Cross multiply to solve for b:
10(33) = b(30)
330 = 30b
b = 330/30
b = 11

Therefore, the solutions to the given equations are:
1) b = 4
2) b = 2
3) b = 36
4) b = 11