I have notes on geometric mean but still have no clue on this business analysis 2372 homework. Please show step by step.

I have notes on geometric mean but still have no clue on this business analysis 2372 homework. Please show step by step.

A mutual fund you purchased in the years 2011-2014 has the following rates of return, in chronological order beginning in 2011:

0.50, 0.30, -0.10, -0.15.

Calculate the geometric mean return. Report your answer as a decimal, NOT a percent, to three decimal places. 

I am not even sure where to start.