General Studies · Number Analogy

Two sets of numbers are given below. In each set, certain mathematical operation(s) on the first number result in the second number, on the second result in the third, and so on. Which of the options follows the same pattern? (NOTE: Operations should be performed on whole numbers. E.g., 13 - Operations on 13 such as adding/subtracting/multiplying can be performed. Breaking down 13 into 1 and 3 is not allowed.) 61 – 70 – 64 – 67 75 – 84 – 78 – 81