3. a) How can you transform the circuitry in Q1(b) to convert it into a carry-lookahead adder? Draw the complete carry-lookahead circuit (in terms of inputs and carries). (20) b) How can you use the five-bit carry-lookahead adder in 'a' as a block to create a twenty-bit adder? Draw the circuit. No need to draw the complete lookahead circuitry. (5)

Fig: 1