I'm either confused about what you're asking, or you're confused about how you might make money writing a call.
So let's look at the simplest case: you write a call (=sell a call), you leave it open to expiration, and the stock is not called away before expiration. Let's denote the TSLA price on the date of expiration "Pe".
- If Pe <= $300, you simply keep the $48 premium (plus interest)
- If Pe > $300, your net payoff is 48 - (Pe - 300). Your break-even is P3=$348; technically unlimited loss as the price goes to infinity.
I think what you're thinking of us writing a covered call, i.e. buying 100 shares of TSLA and sell a call. This has completely flipped payoffs compared to the naked call:
- If Pe <= $300, your net payoff is 48 + (Pe - 255); loss limited at 48 - 255 = (207).
- If Pe > $300, your net payoff is 48 - (Pe - 300) + (Pe - 255) = 48 + 300 - 255 = $93. Your break-even is $207 as the price goes to zero.
So in this simple case, you can see that it's bullish to set up a covered call, i.e. buying equity and writing a call: you lose if the price goes down. You lose less badly than if you simply hold the equity--in fact you do better, as long as the equity's price doesn't rise above $348 from its current $255 level. What you give away is upside: if TSLA has a big price increase, you only participate in the first part of the run-up.
Writing a naked call, OTOH, is bearish: you lose if the price goes up (too much). It's less bearish than shorting the stock outright, because you only lose if the stock price goes up by more than the premium you were paid. (To write naked calls you'll need Level 4 option trading rights or the equivalent at your brokerage, and the calls must be in a marginable account. If the price of TSLA goes up, you might end up having to make a margin call. Definitely not a newbie strategy.)
You can't simply conclude that you earn $45% on the call; it all depends on how the stock price plays out.
Hope this helps!