See links below:
1) the position of the competitive firm: https://www.youtube.com/watch?v=muFSypea2vo&index=52&list=PL-uRhZ_p-BM4XnKSe3BJa23-XKJs_k4KY
2) how a competitve firm maximises profit (MC=MR): https://www.youtube.com/watch?v=0x4f2e5m1Jw&index=53&list=PL-uRhZ_p-BM4XnKSe3BJa23-XKJs_k4KY
3) How total profits are calculated: https://www.youtube.com/watch?v=hl5HqR8bCio&list=PL-uRhZ_p-BM4XnKSe3BJa23-XKJs_k4KY&index=54
4) https://www.youtube.com/watch?v=hl5HqR8bCio&list=PL-uRhZ_p-BM4XnKSe3BJa23-XKJs_k4KY&index=54
5) Monopoly profit maximisation: https://www.youtube.com/watch?v=IEjcTLPtTIY&index=60&list=PL-uRhZ_p-BM4XnKSe3BJa23-XKJs_k4KY
6) The monopoly profit graph: https://www.youtube.com/watch?v=02OUinjL2MI
