Minimum No of 2 X 1 mux required to make A XOR B is 2 and for And gate 1 hence
HALF ADDER = 3 2 X 1 mux required
Full Adder =2 X half adder +OR gate =2 X 3+1=7 2 X 1 mux
Minimum No of 2 X 1 mux required to make A XOR B is 2 and for A'B is 2 hence
Half subtractor =2+2 mux
Full Subtractor =4*2+1=9 mux