It is equivalent to doing two things
1: Buy 300 put and sell 290 put
2: Sell a separate 290 put.
Assume stock closed at 290 at expiration date, then clearly #1 has a value of $10, which equals to spread, and #2 has a value of $0.
However, you also have a credit of $5 when establishing both #1 and #2, so you max profit of this hedge at stock price of 290 is $15. Since the stock you hold declined by $10 from 300 to 290, therefore at this point, you are fully protected at 290, with an extra $5 from that credit.
Now, you will be assigned stock at 290. If stock continues to drop, that $5 credit will protect another $2.5 stock price drop, so your breakeven is 287.5
If you dont care about the temporary stock drop, then you essentially got assigned more stocks at 275 (290 - 15)
Pretty straightforward
