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 : 516 : : 4 : ?

64 68 66 76

66

a : a3 + \(\frac{a}{2}\) 8 : 83 + \(\frac{8}{2}\) = 512 + 4 = 516 4 : 43 + \(\frac{4}{2}\) = 64 + 2 = 66