Convert 63 to 7-bit binary.

Step 1: Convert 63 to 7-bit binary.

Step 2: Convert -64 to 7-bit two's complement.
The range for 7-bit two's complement is $-2^{7-1}$ to $2^{7-1}-1$, which is $-64$ to 63.
The number $-64$ is represented directly as $1000000_2$.

Step 3: Add the two binary numbers.

  0111111  (63)
+ 1000000  (-64)
---------
  1