Urgent help needed with maths question?

Question

please can sombody help me how to answer this quesiton?

make r the subject
A = (pi)r(squared) + 12r / 2

im unsure on how to make a letter the subject when it is featured on both sides.
please can somebody help me?

:] ty

im unsure how to

Answer 1

A = (pi)r^2 + 12r/2
(pi)r^2 + 6r = A
(pi)r^2 + 6r - A = 0
r = [- 6 +- Sq Rt (36 + 4(pi)(A)]/2(pi)

Answer 2

A = πr² + 12r/2

A = πr² + 6r

divide thru by π

A/π = r² + (6/π)r

Complete the square

r² + (6/π)r + 9/(π²) = A/π + 9/(π²)

(r + 3/π)² = A/π + 9/(π²)

(r + 3/π) = ±√(A/π + 9/(π²))

r = ±√(A/π + 9/(π²)) - 3/π
.