Question 743439
You have an order for an 8 gallon aquarium that is 20 inches long and 10.5 inches wide. How deep should the aquarium be? 

this is what I know....

Common aquarium holds 10 gallons.  I know volume of a right rectangular tank is found by multiplying the length of the tank times the width times the height, or V=lwh. I know 231 cubic inches are equal to 1 gallon. 
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What's common is not relevant.
V = lwh & 1 gallon = 231 cu inches is all you need to know.
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V = 20*10.5*h = 8 gal*231 cubic in/gallon
210h = 1848
h = 1848/210
h =~ 8.8 inches