A good answer might be:

              1 11      1  1
   0F4A → 0000 1111 0100 1010
   420B → 0100 0010 0000 1011
   ----    --------------------
           0101 0001 0101 0101  → 0x5155

Additional Addition Practice

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 "A... B... C... D".

QUESTION 9:

Compute the following sum using 8 bits. Is there overflow? 

   1101 0010
   0110 1101
   ---------