ANS:D - 110001

For 15 to be subtracted from 43, 15 need to be converted into 2's complement. Binary equal of 15 is 001111 as to represent 43 we require 6 bits now make the converted binary 's msb to 1.

So to indicate it is -15. Now complement the last 5 bits it will result in 10000 now to get 2's complement add 1 to lsb so it will become 10001 now with msb it will be 110001.