19. A paper airplane was thrown from the top of a tall building. The height of the paper airplane above the ground can be found using the function y'= -1.5x + 60.
where x is the time in seconds the airplane has been in the air. How many
seconds did it take the paper airplane to reach the ground?

20. Write the equation of a line with an undefined slope that goes through the
point (8,4)

21. Write the equation of a line with a zero slope that goes through the point
(1,6).

22. Write the equation of a horizontal line that goes through the point (-3, -6).

23. Write the equation of a vertical line that goes through the point (-11, -20).