The first thing I would do is write an expression for the amount the limo will cost in terms of the number of miles you drive. In this scenario, the cost=.15(mile)+700.
Now is the question, should the limo cost more or less than $750 to stay on budget? The answer is you should spend less than $750. Thus, when writing the inequality, or .15m+700<750. However, you could spend exactly $750 so you inequality should really be .15m+700≤750. Now you just need to solve this for the number of miles you can drive.
First, subtract 700 from both sides and you are left with .15m≤50
Then divide both sides by .15 and you are left with m ≤ 333.33. Thus, the limo can only travel 333.33 miles.