How to find the derivative for calculating water flow rate?

[miaprincess22]

This due today!

Water flows from a tank of constant cross-sectional area 56 ft2 through an orifice of constant cross-sectional area 1.5 ft2 located at the bottom of the tank.
Initially the height of the water in the tank was 20 and its height t sec later is given by the following equation.

2h^(1/2) + (1/23)t -80^(1/2)

How fast was the height of the water decreasing when its height was 8 ft? (Round your answer to two decimal places.)

I thought I was just supposed to find the derivative. I keep getting wrong.

 

[HallsofIvy]

This due today!

Water flows from a tank of constant cross-sectional area 56 ft2 through an orifice of constant cross-sectional area 1.5 ft2 located at the bottom of the tank.
Initially the height of the water in the tank was 20 and its height t sec later is given by the following equation.

2h^(1/2) + (1/23)t -80^(1/2)

How fast was the height of the water decreasing when its height was 8 ft? (Round your answer to two decimal places.)

I thought I was just supposed to find the derivative. I keep getting wrong.

Yes, you are asked for the derivative of h. One problem you have is that what you give is NOT an "equation"! What is that expression supposed to be equal to? Is 'h' in that formula supposed to be the height?