An Astronaut Has Landed on Planet N-40 and Conducts an Experiment

An astronaut has landed on Planet N-40 and conducts an experiment to determine the free fall acceleration on that planet.She uses a simple pendulum that is 0.640 m long and measures that 10 complete oscillations 26.0 s.What is the free fall acceleration on Planet N-40?

A) 4.85 m/s²
B) 1.66 m/s²
C) 3.74 m/s²
D) 2.39 m/s²
E) 9.81 m/s²