When the trader writes a call option, they receive the premium, which in this case is $2. This premium is the trader's immediate cash flow. If the option is held until September and the stock price is $25 at that time, the holder of the call option will exercise the option and buy the stock at the strike price of $20, since it is more profitable to buy the stock at $20 and then sell it at the market price of $25.
As the writer of the call option, the trader will have to sell the stock at the strike price of $20, which means they will lose out on any potential gains above that price. The trader's cash flow in this scenario will be: They will have to sell the stock at the strike price of $20, which will result in a loss of $5 per share ($25 market price - $20 strike price).
The trader received a $2 premium when he sold the call option. Thus, the trader's net cash flow is a loss of $3 per share ($2 premium minus $5 share short loss) multiplied by the number of shares covered by the option contract. In conclusion, if a trader holds the option until September and the stock price at that time is $25, he will immediately receive a $2 premium, but if he has to sell the stock at the strike price, he will lose $3 per share. from $20.