1)

9x = 1581 + 78

9x = 1659

x = 1659 : 9

x = 184 1/3

2)

84 : x = 17 - 5

84 : x = 12

x = 84 : 12

x = 7

3)

267 + a = 8*53

267 + a = 424

a = 424 - 267

a = 157

4)

34 - 4x + 18 = 28

52 - 4x = 28

4x = 52 - 28

4x = 24

x = 24 : 4

x = 6

5)

x - 36 = 408 : 51

x - 36 = 8

x = 8 + 36

x = 44