Answer:
t = 21
Step-by-step explanation:
The ball strikes the groujd when h = 0.

Since time must be positive, t = 21.
Answer:
For number 9)
Interval notation ![(-\infty,3]](https://tex.z-dn.net/?f=%28-%5Cinfty%2C3%5D)
For number 10)
Interval notation:
.
Step-by-step explanation:
On square roots you have to make sure the inside is positive or zero.
So the domain of the first one will come from solving

Subtract 6 on both sides:

Divide both sides by -2 (flip inequality when divide both sides by negative):

The domain is less than or equal to 3.
Interval notation ![(-\infty,3]](https://tex.z-dn.net/?f=%28-%5Cinfty%2C3%5D)
On fractions you have to watch out for dividing by 0.
The domain is all real numbers except when 4x+2=0.
4x+2=0
Subtract 2 on both sides:
4x=-2
Divide both sides by 4:
x=-2/4
Reduce:
x=-1/2
The domain is all real numbers except when x=-1/2
Interval notation:
.
Answer:
15
Step-by-step explanation:
divide the number than multiply by 13