You are given 4-bit ripple carry adders and logic gates you have learnt about in the class (AND, OR, NOT, XOR, XNOR, NAND, NOR). Construct a 12-bit adder/subtractor from the provided components. An input S will determine the type of operation. If S=0, it should add, otherwise subtract. You can use black boxes to represent 4-bit adders for this part of the question.