Complete the analogy 63 : 27 :: 82 : ? by working out the rule that links the first pair.

Write the number backwards and take the smaller from the larger: 63 − 36 = 27. For 82 the reversal is 28, and 82 − 28 = 54. The trap 28 is the reversal itself, with the subtraction left undone. 6 is the difference of the two bare digits, 8 − 2; that rule fails the first pair, where 6 − 3 = 3, not 27. 60 is the difference of the squares of the digits, 64 − 4.