Answer:
the rate of change of the water depth when the water depth is 10 ft is; 
Step-by-step explanation:
Given that:
the inverted conical water tank with a height of 20 ft and a radius of 8 ft is drained through a hole in the vertex (bottom) at a rate of 4 ft^3/sec.
We are meant to find the rate of change of the water depth when the water depth is 10 ft.
The diagrammatic expression below clearly interprets the question.
From the image below, assuming h = the depth of the tank at a time t and r = radius of the cone shaped at a time t
Then the similar triangles ΔOCD and ΔOAB is as follows:
( similar triangle property)


h = 2.5r

The volume of the water in the tank is represented by the equation:



The rate of change of the water depth is :

Since the water is drained through a hole in the vertex (bottom) at a rate of 4 ft^3/sec
Then,

Therefore,

the rate of change of the water at depth h = 10 ft is:




Thus, the rate of change of the water depth when the water depth is 10 ft is; 
Answer:
b, since the others have the input and output on the wrong sides
Answer:
m = -3/2 and b = 4
Step-by-step explanation:
m = slope and u go down 3 and over 2 so its -3/2
b = your y intercept and its intercepting through 4 on the y-axis
To determine how much will it take to clean a 120ft driveway considering that it took him 2hs to clear 10ft and that the cleaning rate is constant, you can use cross multiplication:
10ft______2hs
120ft_____xhs
If the cleaning rate is the same, then the ratios between both are the same:

From this expression, you can determine the time by multiplying both sides of the equal sign by 120

It will take him 24 hours to clear the 120ft driveway.