I need help with this question for homework:

The adder below adds two 16-bit numbers X and Y (ie. S=X+Y), where X=X15X14 XiXo and Y-Y15Y14...YiYo. Assume we are using two's complement representation for our signed numbers, in which flipping all the bits of a number Y and adding one to it will give -Y. Modify the circuit below by including a signal P that picks whether the circuit will add them as X+Y, or subtract them as X-Y- X+(-Y). Suppose when P-0 the circuit will add and when P-1 it will subtract. Hint: Q XOR 1 flips Q (that is Q XOR 1 = Q') 15 15 Y. X Carry Out 15 2 FA FA FA Carry In