Here we can just convert the hexadecimal numbers to binary numbers easily, then again convert the resultant binary number to hexadecimal number.
F == 15 == 1111
D == 13 == 1101
So FD == 11111101
In the same way,
88 == 10001000
So
FD - 88 = (11111101) - (10001000)
= (11111101) + 2's complement of (10001000)
= (11111101) + (01111000)
= 01110101
= 75 ( in hexadecimal)
So A is the correct answer.
Kindly suggest, if there is any mistake in the process.