9. \( P=2(\ell+w) \), when \( \ell=7 \mathrm{yd} \) and \( w=4 \mathrm{yd} \)

To find the perimeter \( P \) of a rectangle using the formula \( P=2(\ell+w) \), you simply plug in the values for the length \( \ell \) and the width \( w \). Here, \( \ell=7 \mathrm{yd} \) and \( w=4 \mathrm{yd} \). So, \( P = 2(7+4) = 2(11) = 22 \mathrm{yd} \). Voilà! The perimeter is 22 yards! Now let’s think about real-world applications! Understanding how to calculate the perimeter is super handy in everyday situations. Whether you're fencing your backyard, planning a garden layout, or even wrapping gifts, knowing the perimeter can help you make smart decisions on materials needed. So go ahead, measure those dimensions, and see your space come to life!