Bill's new porch is rectangular, with an area of 50 square feet. If the length of the porch is two times the width, what is the perimeter of the porch?

1. The formula for the area of a rectangle is:

 A=LxW

 L: The lenght of the rectangle (L=2W).
 W: The width of the rectangle.

 2. Let's substitute L=2W into the formula A=LxW:

 A=LxW
 A=2WxW
 A=2W²

 3. When we clear "W", we obtain:

 W²=A/2
 W=√(A/2)

 4. We already know the value of "A", so:

 W=√(50 ft²/2)
 W=√(25 ft²)
 W=5 ft

 5. Now, we must substitute the value of "W", into L=2W:

 L=2W
 L=2(5 ft)
 L=10 ft

 6. The perimeter of a rectangle is:

 P=2L+2W

 7. We know the value of "L" and "W", therefore:

 P=(2x10 ft)+(2x5 ft)
 P=20 ft+10 ft
 P=30 ft

 What is the perimeter of the porch? 

 The answer is: 30 ft