A rectangular large fish tank was filled with water to a height of 8 cm. Its rectangular base was 40 cm by 25 cm wide. When 14 liters of water were poured into the fish tank, the water level rose to 0.8 of the height of fish tank. What was the height of the tank?
The fish tank has a rectangular base with dimensions 40 cm by 25 cm, so its volume is 40 cm * 25 cm * 8 cm = <<40*25*8=8000>>8000 cm^3.
Since 1 liter is equal to 1000 cm^3, then 14 liters is equal to 14 * 1000 cm^3 = <<14*1000=14000>>14000 cm^3.
Let x be the height of the fish tank.
Thus, 14000 cm^3 is equal to 0.8 * x * 40 cm * 25 cm.
So we have the equation 14000 cm^3 = 0.8 * 40 cm * 25 cm * x.
Dividing both sides of the equation by 0.8 * 40 cm * 25 cm, we get x = 14000 cm^3 / (0.8 * 40 cm * 25 cm) = 14000 cm^3 / (8 cm * 100 cm) = 14000 cm^3 / 800 cm = 17.5 cm.
Therefore, the height of the fish tank is 17.5 cm. Answer: \boxed{17.5}.