4. Implement a digital circuit for the following: [5 marks] A) Build a two-input NOR gate using only NAND gates (Hint: refer to lecture 3 where we build an OR gate using NAND gates and think how you can make a NOR gate, whein you have OR gate). B) Build a two-input NAND gate using only NOR gates (Hint: refer to lecture 3 where we built an AND gate using NOR gates and think how you can make a NAND gate when you have AND)