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. [10] b) Using the 4-bit adder discussed in class, show how you can simplify the circuit if you knew the circuit would always be adding 3. Start with the 4-bit ripple carry adder, set the value on input 'B' to the constant 3, and then reduce the logic gates because of the constant value of 3. [101 c) Specify the worst-case path and worst-case gate delay for your system in (a). [5] d) Specify the worst-case path and worst-case gate delay for your system in (b). [5]