We can also do subtraction using adders. As we have already studied that we can do subtraction by 2’s compliment method in which we add 2’s compliment of subtrahend to minuend and 2’s compliment can be found by inverting all bits of subtrahend and then adding one. So we have to do as

F= A – B = A + 2’S compliment of B = A + 1’S compliment of B + 1

So we give A at one input, invert of B at 2nd input and give 1 at carry. Hence we implement the above function.