The roots of 54 are: 1 and 54, 2 and 27, 3 and 18, 6 and 9, then it restarts all over again.
The two numbers have to multiply up to 54, and add up to 3. 9 and 6 have a difference of 3, and the multiplied sum is negative, so this is your pair.
9 and -6 fit this criteria, since they add up to 3 and multiply to 64.
