Hey there!
The answer is 4 meters, or 4 m.
The formula for volume is lwh, or Length * Width * Height, so we can set up an equation plugging in the values we know:
lwh = V
l(2)(10) = 80
Simplify:
20l = 80
Divide both sides by 20:
l = 4
Have a terrificly amazing day! :)