The graph shows the volume of water, in gallons, remaining in a storage tank as it drains at a constant rate. The x-axis represents the time in hours since the draining began, and the y-axis represents the volume of water in gallons.

How many gallons of water will drain from the tank between 2 hours and 8 hours after the draining process begins?

[Graph Description: A line segment starts at (0, 500) and goes down to (20, 0). The x-axis is 'Time (hours)' from 0 to 25, with major ticks every 5 hours. The y-axis is 'Volume (gallons)' from 0 to 600, with major ticks every 100 gallons. The line passes through (4, 400), (8, 300), (12, 200), (16, 100).]