2/3n - 6 = 18 ( this is a 2 step equation )

 See below

Step-by-step explanation:

4) You made an error in step 3

Step 1: -x³ + 22x² - 121x = 0

Step 2: -x(x² - 22x + 121) = 0

Step 3: -x(x - 11²) = 0       Error!

           -x(x - 11)² = 0        Correction

Step 4: -x = 0     (x - 11)² = 0

Step 5:    x = 0      x = 11

15) Your work is correct

    n = 8, n = -9      BOTH answers are correct

n = 8      Error!  

              n = 8, n = -9    Correction

18) The formula is: h(t) =at² + vt + h(0)

h(t) = -4.9t² + 24.5t + 117.6      option 3

19) Now that you have the correct equation, you can use the quadratic formula to solve for t

t = -3, t = 8

Since time cannot be negative, t = -3 is not valid

t = 8    option 1

20) It is given that h(t) = 49

Equation: 49 = -4.9t² + 24.5t + 117.6

                 0 = -4.9t² + 24.5t + 68.6

Use the quadratic equation to solve: t = -2, t = 7

Since time cannot be negative, t = -2 is not valid

t =7