Let's analyze the problem.

Given:

• The garden is a triangular shape, and its perimeter is 36 feet.
• The sides of the triangle are:
  • 15 feet,
  • 5 feet,
  • 3 feet,
  • And one unknown side, which we need to find (denoted as "? ft").

Solution:

The perimeter of a triangle is the sum of all its sides. So:

$P = 15 \, \text{ft} + 5 \, \text{ft} + 3 \, \text{ft} + \text{? ft}$

Since the total perimeter is 36 feet, we can set up the equation:

$15 + 5 + 3 + ? = 36$

Simplify:

$23 + ? = 36$

Now, solve for the unknown side:

$? = 36 - 23 = 13 \, \text{feet}$

Thus, the missing side is 13 feet.

Would you like further details, or do you have any questions? Here are 5 related questions for practice:

1. How do you calculate the perimeter of any polygon?
2. What is the difference between the perimeter and area of a shape?
3. If one side of the triangle were increased by 2 feet, how would the perimeter change?
4. How would you solve for an unknown side if given angles and one side of a right triangle?
5. Can the triangle inequality theorem help in verifying the side lengths?

Tip: Always ensure that the sum of any two sides of a triangle is greater than the third side—this is called the triangle inequality theorem.