4 marks for explanation - explanation of both types profit and definition of windfall tax
4 marks for Analysis - application as to why the firm makes supernormal profit and how windfall tax affects it
2 marks for a graph - monopoly graph
Supernormal profit is profit that is in excess of costs meaning that total revenue made is more than the total costs indicating that it is above the break-even point. Whereas, normal profit is the minimum amount of profit required for a firm to cover its costs and stay in business.
analysis: since it's an electricity company it's most likely a collusive oligopoly and hence they produce at profit maximisation being MR = MC you can then draw the monopoly graph and show the area of supernormal profit.
Subsequently, when this supernormal profit exceeds a certain amount government imposes a windfall tax which becomes a source of government revenue but will have no effect on the equilibrium price of the firm as they will continue as profit maximisers.
Hope this helps- let me know if anything doesn't make sense.