Given that the height of the candle in inches is modeled by this equation:
You know that "x" is the number of hours that have elapsed and "y" is the height of the candle.
You need to calculate the time (in hours) the candle last before it burns completely. Therefore, you need to substitute this value of "y" into the equation:
Then, by substituting it into the equation and solving for "x", you get:
Hence, the answer is: Third option.