Two equations with infinite solutions would look the exact same. Example:
y=mx+b
y=mx+b
Example 2
y=2x+5
y=2x+5
For an equation with no solution they would have the same slope but different y intercepts. An equation with same slope and same y intercepts would have infinite solutions.
I think you probably divide 7,200 gallons by 81 gallons since it's asking how many in one.