If the area of a circle is increased by a factor of 9, the circumference of that circle will be increased by what factor?

Question

a. 3
b. 6
c. 9
d. 18
e. 81

please answer and explain

Answer 1

A = pi r^2

A' = 9 pi (r)^2 = pi R^2

so R^2/r^2 = 9
R/r = 3

circumference proportional to radius
so
THREE times