To solve this problem:

1. Perimeter of a square is given as $P = 4 \times \text{side length}$.

2. The side length is $2x + 3$, and the perimeter is 36. Therefore: $4 \times (2x + 3) = 36$

3. Simplify and solve for $x$: $8x + 12 = 36$ Subtract 12 from both sides: $8x = 24$ Divide by 8: $x = 3$

So, $x = 3$.

Would you like further details or have additional questions? Here are five related queries:

1. How do we verify the solution for $x = 3$?
2. What happens to the perimeter if $x$ is doubled?
3. How does this problem change if the side length formula is altered?
4. Can you generalize this for different perimeters?
5. How would the area of the square be calculated with $x = 3$?

Tip: Always double-check your work by plugging the solution back into the original formula!