A tank can hold 40,000 gallons of water. If 500 gallons of water are used each day, write the equation that represents the amount of water
in the tank x days after it is full.

I’m not exactly sure what you are asking but it could be either of these two things

1) 40,000-500(x)
this is the equation you could use

or

2) the tank will be empty after 80 days
this is to solve the problem

to check your work
40,000=500(80)
40,000=40,000
this way it checks out

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