What is the radius of a circle if its area is numerically equal to four times its circumference?

Question: What is the radius of a circle if its area is numerically equal to four times its circumference?

Solution:
Let the radius be r.

Area = πr²
Circumference = 2πr

According to the question,
πr² = 4 × 2πr
⇒ r² = 8r
⇒ r² - 8r = 0
⇒ r(r - 8) = 0
⇒ r = 8 (taking the positive value)

∴ The radius of the circle is 8 units.