To solve problems like this, we must simply break it down and read each part carefully. We can also set it up as a math problem to make it easier to visualize.
The elevator starts on the twentieth floor, so we will represent that with 20.
20
It goes down 11 floors, so we can represent that with a -11.
20-11=9
Now we are on floor 9. Then, we go up 5 floors, so we can represent that with a 5.
9+5=14
Using the math above, we can see the elevator is on the 14th floor.
Refer the attached figure for the graphic representation of the given quadratic equation.
<u>Step-by-step explanation:</u>
Given expression:

To find:
The graphic representation of the given quadratic function
For solution, plot the graph to the given quadratic equation.
The standard form of the equation is

When comparing with given quadratic equation,
a = 1, b = - 8, c = 24
Axis of symmetry is 
By applying the values, the axis of symmetry of given equation is

The vertex form of quadratic equation is 
Where, (h,k) are the vertex.
Convert the quadratic equation into vertex form.
By completing the square,



On comparison,
(h , k) = (4 , 8)
Now, plot the equation with vertex (4,8) [refer attached figure].
Answer:
x=11
Step-by-step explanation:
Using the Exterior Angle Theorem. . .
(3x+8) + (2x+9) = (8x-16)
Solve to get x = 11