Two's complement of hexadecimal
If you're a bit acquainted with hex you don't need to convert to binary. Just take the base-16 complement of each digit, and add 1 to the result. So:
F - F = 0
F - 3 = C
F - A = 5
F - 1 = E

So you get 0C5E. Add 1 and here's your result: 0C5F.