If I sustained a cervical sprain/strain injury from a bus accident and my $medical bills are $7,200 with $900 of lost income, how much is my settlement?

There is no hrad and fast answer. IF you went to trial and won, the most you'd get would be the sum of your medical bills (the out-of-pocket, or not paid by insurance, part), lost wages, other out-of-pocket expenses, and possibly some "pain and suffering" if you experienced weeks or more of pain, impairment, disability, etc. Your write about $8,100 of costs; for the sake of this example, lets' assume you also had some out of pocket costs (e.g. had to take cabs or car services; had to hire someone to clean for you) and might get something for pain and suffering; I'll round to to $10,000.

When you settle, you accept less than that. You accept less, because you get the money faster, without the cost and uncertainty (you don't always win, even with good cases) of trial. And paying less is the other side's incentive to settle. Usually, the earlier in the process you settle, the less you receive (which makes sense: when you settle early, you incurred less costs and delays).

Generally, settlement range from 25% to 60% of the amount at stake, so a settlement in your case, using the $10,000 figure I put out above, might be $2,500 to $6,000, with the amount depending on when you settle, strength of your case, and the personality of the decision maker on the other side. You'll rarely get the full amount you're seeking, since for that, they'll typically go to trial--why settle if they are not saving anything?