please help me answer this. please answer on an ipad or piece of paper step by step.

A Martian wants to determine the strength of the gravitational field on his home planet. His only equipment is a simple pendulum, which is 1 meter long. He sets up the apparatus and finds that it completes 40 oscillations in 100 seconds. Find the strength of the gravitational field on Mars Factor of change question - what would happen to the period of a pendulum if you cut its length in half AND doubled the strength of the gravitational field