How many square feet of wallpaper will she need to buy?

Question

Regina wants to cover one wall of her room with wallpaper. The wall is 9 feet high and 15 feet wide. There is a doorway in the wall that is 3 feet wide and 7 feet tall. How many square feet of wallpaper will she need to buy?

Answer 1

(9)(15) - (3)(7) = ?

This is my studied assumption.

Answer 2

L_w = 15 (ft) ← given

W_w = 9 (ft) ← given

L_w - length of the wall

W_w - width of the wall

W_d = 3 (ft) ← given

H_d = 7 (ft) ← given

W_d - width of the doorway

H_d - height of the doorway

Calculating the area of the wall including the doorway:

A_w = L_w • W_w = 15 • 9 = 135 (ft²)

Calculating the area of the doorway:

A_d = W_d • H_d = 3 • 7 = 21 (ft²)

Calculating the area to cover with wall paper:

A_w - A_d = 135 - 21 = 114 (ft²)