Answer:
15 sheets
Step-by-step explanation:
The wall is rectangular; thereofre, its area is the product of its height and length.
The area of the wall is

Now the area of one sheet of drywall is

Now we ask ourselves: how many sheets of drywall fit into an area of 450 square ft?
The answer is found by dividing the area of the wall by the area of one sheet:

This means that 15 sheets are needed to cover the wall.