Question: 14. Find the missing side length of the rectangle $k$.
$P = 20$ m
$3$ m
$k$
$k =$
1. **State the problem:** We need to find the missing side length $k$ of a rectangle where the perimeter $P$ is $20$ meters and one side length is $3$ meters.
2. **Recall the formula for the perimeter of a rectangle:**
$$P = 2 \times (\text{length} + \text{width})$$
3. **Assign known values:**
Let the length be $k$ and the width be $3$ meters.
4. **Write the equation using the perimeter formula:**
$$20 = 2 \times (k + 3)$$
5. **Divide both sides by 2 to isolate the sum:**
$$\frac{20}{2} = \cancel{2} \times (k + 3) \div \cancel{2}$$
$$10 = k + 3$$
6. **Subtract 3 from both sides to solve for $k$:**
$$10 - 3 = k + 3 - 3$$
$$7 = k$$
7. **Final answer:** The missing side length $k$ is $7$ meters.