Answer: E. (126 + 10.5x) square feet
Explanation:
The formula for determining the area of a rectangle is expressed as
Area = length × width
The length of a living room is 12 feet and its width is 10 1/2 feet. If the length of the room is being expanded by x feet, then the new length would be (12 + x) feet
Therefore, an expression to represent the new area of the living room in square feet would be
10.5(12 + x)
The expanded form of the expression would be
(126 + 10.5x) square feet