The average (arithmetic mean) of 330, 360 and 390 is :

Answer: Option B

According to the question,
$$\begin{array}{rl}& \Rightarrow \frac{3^{30}+3^{60}+3^{90}}{3}\\ & \Rightarrow 3^{29}+3^{59}+3^{89}\end{array}$$