Select the option that is related to the fifth number in the same way as the second number is related to the first number

Select the option that is related to the fifth number in the same way as the second number is related to the first number and fourth number is related to third number.

31: 3 ∷ 75: 35 ∷ 54: ?

A.            19

B.            9

C.            20

D.            21

Sol:

31: 3

⇒ 3 × 1 = 3 …(i)

75: 35

⇒ 7 × 5 = 35 …(ii)

54: 20

⇒ 5 × 4 = 20 …(iii)