Calculate the Perimeter of an Isosceles Trapezoid with Sides 3, 5, and 7

To find the perimeter of the isosceles trapezoid, consider the following steps:

• Step 1: Identify the given side lengths: The top base of the trapezoid is $3$, each of the slanted sides is $5$, and the bottom base is $7$.
• Step 2: Apply the perimeter formula: The perimeter $P$ is the sum of all side lengths: $P = 3 + 5 + 5 + 7$.
• Step 3: Perform the calculation: Add the side lengths together:
  $3 + 5 + 5 + 7 = 20$

Therefore, the perimeter of the isosceles trapezoid is $20$.