The changing rate of the amount of water in the watering can is a constant rate of 0.15 gallon per minute.
The initial volume of water in the can at time = 0 is 5 gallons
The function will be a linear function in the form of
where
is the volume of water in the can after 
minutes
is the changing rate
is the initial volume when time is 0
Substitute all the values into the form we have
The initial volume of water in the can at time = 0 is 5 gallons
The function will be a linear function in the form of
Substitute all the values into the form we have