Select the option that is related to the third number in the same way as the second number is related to the first number. 8 : 16  : :  20 : _____

30 40 25 35

40

Logic is : 2n : 4n.  In this: 2 × 4 = 8 4 × 4 = 16,  Same as: 2 × 10 = 20 4 × 10 = 40