What is the equation used to solve this problem? what is k equal to

Question

Find the constant of variation k for the stated condition.

A varies directly as the square of r, and A = 1386 when r = 21

ive tried every equation i can think of and all the answers have come back wrong.

what does k equal to?

Answer 1

1386 = k(21)^2 = 441k

k = 1386/441 = an approximation for pi

A = (1386/441)r^2 = about pir^2 = Area of a circle with radius = r

but 1386/441= 3.142857142857142857..... is slightly less than pi= 3.141593...