5. The ripple carry adder below adds two 4-bit 2's complement numbers X and Y (i.e. S=X+Y), where X=X3X2X1Xo and Y=YzY2Y Yo a) (10 pts) Modify this circuit in a way that it can perform subtraction. y3 y1 C. C. Con Cia Cor Full Adder Full Adder Full Adder Full Adder b) (10 pts) Demonstrate the subtraction by showing the trace of the circuit for performing: 0011-0111. If you fail part a, show the trace of 0011+0111 on the originally given circuit