Water tank holds $20,000 how long will it take for the water level to reach 6000 gallons if the water is used at an average rate of 500 gallons per day

Is the $20,000 supposed to be 20,000 gallons???

If so,
20,000-500x=6,000
would be your equation needed to solve this.

Subtract your 20,000 from both sides.
This should leave you with a new equation of
-500x=-14,000

Divide both sides by -500 to leave a single x variable on one side of the equation. You should be left with a new equation of
x=28

That's it!
It takes 28 days for the water level to reach 6,000.