Answer:
B. 
Step-by-step explanation:
Let l represent length of rectangle and w represent width of rectangle.
We have been given four formulas for the perimeter of rectangle. We are asked to choose the formula that displays a common student error for finding the perimeter.
We know that perimeter of a polygon is sum of all sides of the polygon. We also know that rectangle is polygon having two sets of equal sides.
The perimeter, P, of rectangle will be sum of its all sides that is:

Combine like terms:

Factor out 2:

Upon looking at our given choices, we can see that formula represented by option B displays a common student error for finding the perimeter.
Answer:
X = 3
You're welcome.
Step-by-step explanation:
I do not see anything wrong with it
Actual area of the rectangular building = 5040 feet²
Step-by-step explanation:
Length of the rectangular building = 7 feet
Width of the rectangular building = 5 feet
Now, The building is made with a scale factor of 12
So, Actual length of the rectangular building = 84 feet
Actual width of the rectangular building = 60 feet
Now, Actual area of the rectangular building = Length × Width
⇒ Actual area of the rectangular building = 84 × 60
⇒ Actual area of the rectangular building = 5040 feet²