Answer:
It use 1.25 gallons of water per second
Step-by-step explanation:
Amount of water used for car wash in 40 seconds = 50 gallons
Amount of water used for car wash in 1 seconds = 
Amount of water used for car wash in 1 seconds = 
So, Amount of water used in 1 second is 1.25 gallons
So, Unit rate = 1.25 gallons per second
Hence it use 1.25 gallons of water per second