When subtracting two numbers, we also use the 2s - complement system. The number to be subtracte d (the subtrahend) is changed to its 2s - complement and then added to the minuend (the number the subtrahend is being subtracted from). Construct a circuit that performs this task. The input s of the circuit should be two four bit numbers of which the first bit is the sign bit and a control input which determines whether these number are added or subtracted from each other. Demonstrate that it works.