1 11 1 1 0F4A → 0000 1111 0100 1010 420B → 0100 0010 0000 1011 ---- -------------------- 0101 0001 0101 0101 → 0x5155
The carry out of zero from the left column in the binary addition indicates that the sum can be contained in that number of bits
Sometimes a hex addition problem is easy enough to do without converting to binary:
014A 4203 ---- 434D
It may be helpful to use your digits (fingers) in doing this:
to add A+3 extend three fingers and count