A 10 inch-candle burns at a linear rate. It measures 9 inches two hours after it was lit. Which equation can be used to find the length of the candle, y, in inches after x hours it was lit?
1. y = 10 - 0.5x
2. y = 10 - 4.5x
3. y = 10 - 9x
4. y = 10 - 2x