Kenny need to buy 4 quarts.
It cost $14.
Solution:
The mailbox is splitted into two shapes.
One is rectangle and the other is hemisphere.
Length of the rectangle = 2.4 ft
Width of the rectangle = 1.5 ft
Height of the rectangle = 3 ft
Surface area of the given rectangle
= 2(lw + wh + lh) – lw
= 2(2.4 × 1.5 + 1.5 × 3 + 2.4 × 3) – (2.4 × 1.5)
= 2(3.6 + 4.5 + 7.2) – 3.6
= 2(15.3) – 3.6
= 27
Surface area of the given rectangle = 27 square feet
Radius of the hemisphere = 1.2 ft
Curved surface area of hemisphere
= [tex]2\pi r^2[/tex]
[tex]=2 \times 3.14 \times 1.2 \times 1.2[/tex]
= 9.0432 square feet
Curved surface area of hemisphere = 9.0432 square feet
Total surface area of the mailbox = 27 + 9.0432
= 36.0432 square feet
To find how many quarts are needed to cover the mailbox.
1 Quart covers = 10 square feet
36.0432 sq. ft = 36.0432 ÷ 10
= 3.60432 quarts
≈ 4 quarts (approximately)
Hence Kenny need to buy 4 quarts.
Cost of 1 quart = $3.50
Cost of 4 quart = 4 × 3.50
= 14
Hence it cost $14.
