I have a problem with the perimeter of a pool expressed in an unknown which corresponds to "x"
The first thing to do is to pose the corresponding equation, this corresponds to section A of the question
For the length, we have a representation of twice the width minus 6, i.e. 2x-6
For the width we simply have x
Remember that the sum of all the sides is equal to the perimeter which is 84, However, we must remember that in a rectangle we have 4 sides where there are two pairs of parallel sides, so we must multiply the length and width by 2
Now we can represent this as an equation

This is the answer A
Now let's solve the equation for part B.


In conclusion, the width of the pool is 16