Culvert is a tunnel, therefore we can use the volume and area formula of a cylinder.
Circumference is given such as 280 cm and the circumference formula of a circle is C = 2*pi*r
Solving for the radius, we have:
280 = 2*3.14*r
r = 280/2*3.14
r = 44.59 cm
Area of one end:
Area = pi*r²
Area = 3.14 * 44.59²
Area= 6,243.2 cm²
The total area is times two of area since there were two ends in the culvert.
Total area = 6243.2 * 2
Total area = 12,486.32 cm²
