Question :- Find the circumference of a circle known that area of the circle is 153.86 ?
The circumference of a circle is $\displaystyle 2\pi r$
The area of a circle is $\displaystyle \pi r^2$
You know that the area of the circle is equal to 153.86.
Using the above formula for the area a circle, you should be able to find the radius (r), and plug it into the formula for the circumference of a circle