A) Does any graph show a proportional relationship?
Yes, the graph for Tank B.
B) The number of gallons at the 1 minute mark is 300. The "unit rate" is
300 gal/min
_____
The graph of a proportional relation is a straight line through the origin. That of Tank A has a non-zero y-intercept, so is not a proportional relation. The graph of Tank B is a proportional relation.