Alandscaper has 125 tiles to build a square patio. the patio must have an area of at least 80 sq. ft.
a what are the possible arrangements for the patio
b how many tiles were not used

The area of a square is given by multiplying the length and the width
Since the sides of a square are all equal, we will end up multiplying two numbers that are the same

We want the area of the patio to be in between 80 and 125

Think of the square numbers between 80 and 125
8 × 8 = 64
9 × 9 = 81
10 × 10 = 100
11 × 11 = 121
12 × 12 = 144

The possible numbers of tiles we could use is 

81 tiles with 125 - 81 = 44 tiles left over
100 tiles with 125 - 100 = 25 tiles left over
121 tiles with 125 - 121 = 4 tiles left over