Part (a):
=======
6 : 9 = x : 72
By using cross multiplication
∴ 9 x = 6 * 72
∴ 9 x = 432
∴ x = 432/9 = 48============================================
Part (b):
=======
8 : 3 = 40 : x
By using cross multiplication
∴ 8x = 3 * 40
∴ 8x = 120
∴ x = 120/8 = 15============================================
Part (c):
=======
x : 55 = 3 : 5
By using cross multiplication
∴ 5 x = 3 * 55
∴ 5 x = 165
∴ x = 165/5 = 33============================================
Part (d):
=======
33 : x = 11 : 5
By using cross multiplication
∴ 11 x = 5 * 33
∴ 11 x = 165
∴ x = 165/11= 15============================================