Answer:

For this case we know that
represent the radius,
the height and the rate given is:


And replacing we got:

And that represent 
Step-by-step explanation:
For a tank similar to a cylinder the volume is given by:

For this case we know that
represent the radius,
the height and the rate given is:

For this case we want to find the rate of change of the water level when h =6m so then we can derivate the formula for the volume and we got:

And solving for
we got:

We need to convert the rate given into m^3/min and we got:

And replacing we got:

And that represent 
The answer is 6.63 Hope this helps!
3/20T of mulch. Each Flower bed will contain 3/20 tons of mulch
Y = -3x + b
Plug in points
4 = -3(-2) + b
4 = 6 + b, b = -2
Solution: y = -3x - 2