To create A NAND B gate, use two 2to1 mux. First mux is used to create A AND B(AND gate), that is, first mux output is 0 if select bit(B)=0, and A if select bit(B)=1 And the output of first mux is connected to select bit(A AND B) to the second mux. that is, second mux output is 1 if select bit(A AND B)=0, and 0 if select bit(A AND B)=1. Thus, first mux is A AND B(AND gate) and second mux is Inverter.