A square pool is surrounded by a concrete deck A square pool of area $144 \, \text{m}^2$ is surrounded by a concrete deck of area $25 \, \text{m}^2$. What is the perimeter of the outside of the deck?
So, the side of square pool $=\sqrt{144\ M^2}=12\ M$

Assuming the deck to be also square,

if the side the deck is $a\ M,$ the area of the deck with the pool $=a^2\ M^2$  

So, the area of the deck $=(a^2-144)\ M^2$

Can you take it home from here?
the area of the pool is 144m^2. The area of the concrete area surrounding the pool is 25m^2. The total area of the concrete block and the pool is 144m^2+25m^2=169m^2.

Now to find the length of each side of a square that includes the pool and concrete.

sqrt(169m^2)= 13 m

Perimeter of the square is 13m
Formula for perimeter of square is P=4a

Formula for square

P=4a
P=4(13m)
P= 52m 

Verify

12m + 2x= 52
x=20