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
