Q1:

Convert each of the decimal numbers to 8-bit two's-complement form and then perform subtraction by taking the two's-complement and adding.

ANS:B - 0000  1110

The given answer is right because convert 18 and 4 in 8 bit that means 18 = 0001 0010.

4 = 0000 0100.

Now convert 4 into 2's complement i.e 1111 1011.

+ 1.
-----------.
1111 1100.

Now add this by 18.

0001 0010.
+1111 1100.
-------------.
1 0000 1110.

Neglect carry hence we got the answer.