It is given in the question that,

Since we have the value of r given, so we have to use the formula to find the nth term of the geometric progression, which is

Substituting the values of a and r, we will get

So the correct option is the third option .
8.75 or C in your screen is the answer. Simply multiply the length X width.
12^2+x^2=15^2
144+x^2=225
- 144 -144
=81= 9
X=9
To find the perimeter it is 2 X Width + 2 X the length = 84
32+ 2 X the length = 84
2 X the length = 52
Therefore the length is 26cm