Assuming ":" means division, solve each:

1) 3*a - 7 = 20
3a = 27 → a = 9

2) $24+d$ : 8 = 7 → $24+d$/8 = 7
24 + d = 56 → d = 32

3) b : 5 + 8 = 17 → b/5 + 8 = 17
b/5 = 9 → b = 45

4) 63 : $14-x$ = 7 → 63/$14-x$ = 7
14 - x = 9 → x = 5

5) 32 - 16 : n = 30 → 32 - 16/n = 30
16/n = 2 → n = 8

Solutions: a = 9, d = 32, b = 45, x = 5, n = 8.