The two triangles are similar, which means the ratios of corresponding sides are equal.

Therefore $\frac{2}{4} = \frac{3}{x} \rightarrow x=6$

Since you now know that $x = 6$, you can determine the diameter and radius of the circle.

Radius $= 4$

Area $= 50.27$ square units
Circumference $= 25.13$ units