Answer:
Third option: 12x^2+8x+25
Step-by-step explanation:
s1=8x^2
s2=4x^2+15
s3=8x+10
Total perimeter of the pool edge: P
P=s1+s2+s3
Replacing s1, s2 and s3 in the formula above:
P=(8x^2)+(4x^2+15)+(8x+10)
P=8x^2+4x^2+15+8x+10
Adding like terms:
P=12x^2+8x+25
Answer:

Step-by-step explanation:
Given
Let the number be x
So:

Required
Using trial and improvement, find x
This implies that we keep guessing the values of x until we get a value that match the equation.
Let

So, we have:


Take the square root of 625



Let

So, we have:


Take the square root of 729



At this point, we can conclude that x is approximately 729 because

So:

0.52944444444 you can simplify the decimal and you will have the answer
Add (or subtract) a number from both sides.
Multiply (or divide) both sides by a positive number.
Simplify a side.