The area of a rectangular classroom is 420 square feet. If the length and width of the classroom are multiplied by 3, what will be the area of the new classroom?

A:1640 ft B:1720 ft C:2840 ft D:3780 ft

D. 3780

When you multiply the sides my a constant, the area multiplies by the constant squared.

ex. sides multiplied by 3, area multiplied by 9.

D: 3780 square feet

Step-by-step explanation:

Let the length be L. Let the width be W.

The area of a rectangle is length times width, so

A = LW

The area is 420 square feet, so

LW = 420

Now you multiply the length by 3 and multiply the width by 3.

The length is now 3L, and the width is now 3W.

The area of the new rectangle is the new length times the new width.

new area = 3L * 3W

new area = 3 * 3 * LW

new area = 9 * LW

LW was the original area, and it is 420 square feet, so the new area is 9 times the old area.

new area = 9 * 420 square feet

new area = 3780 square feet