Alexis has a rectangular piece of red paper that is 4 centimeters wide. It's length is twice it's width. She glued a rectangular piece of blue paper on top of the red piece measuring 3 centimeters by 7 centimeters. How many square units of red paper will be visible on top?

for the rectangular red paper:

w₁ = width of the red paper = 4 cm

L₁ = length of red paper = 2 w = 2 x 4 = 8 cm

A₁ = area of the red paper = L₁ w₁ = 8 x 4 = 32 cm²

for the rectangular blue paper:

w₂ = width of the blue paper = 3 cm

L₂ = length of blue paper = 7 cm

A₂ = area of the blue paper = L₂ w₂ = 7 x 3 = 21 cm²

area visible is given as

A = A₁ - A₂ = 32 cm² - 21 cm² = 11 cm²

so 11 square units of red paper will be visible on top