Here in the word MADRAS, every single letter is coded as the next letter of the alphabet.i.e, M next letter N,A next letter B and so on.so,the results is NBESBT.
similarly the word BOMBAY, every single letter is coded as the next letter of the alphabet.i.e, B next letter C,O next letter P and so on.so,the results is CPNCBZ. i.e, option (b).