We are given that two tanks are draining in a linear form. To determine the rate of draining we need to determine the slope of the lines for each tank. The slope is given by the following formula:

Taking a pair of points from the table:

Replacing in the formula:

Solving the operations:

For tank Y:

Replacing in the formula:

Solving the operations:

Therefore, the rate of change of tank X is 2 gallons/min and tankY 1.5 gallons/min. Tank X has a greater rate of drain.
The difference is:

The difference is 0.5 gallons/min.