Find the surface area of a sphere with a circumference of 155 mm. Round to the nearest tenth.

Help please

2 answers

c = 2pi r
so,
r = c/2pi

a = 4pi r^2 = 4pi (c/2pi)^2 = c^2/pi

a = 155^2/pi = 7647.4
Can someone answer this question with the circumference being 180?