Answer:
.
It means that 673 of 9 inch tiles are required to cover an area of 400 square feet, when spacing the tiles a quarter inch apart.
Step-by-step explanation:
Given:
The function relating number of 9 inch tiles required and area to cover is:

Now, plug in 400 for
to evaluate
.

Therefore, Don required 673 of 9 inch tiles to cover an area of 400 square feet, when spacing the tiles a quarter inch apart.