The water level in a glass decreases 0.4 cm each hour due to evaporation. At the beginning of the experiment, the water level is 12.6 cm. Let x represent time, in hours, elapsed since the beginning of the experiment and let y represent the water level, in centimeters.

Part A

Construct a linear function, using x and y from above, that determines the water level at a given time, in hours, after the experiment begins.

Part B

How many hours does it take for all of the water to evaporate?