Please help me understand how the answer is C showing work using formulas or financial calculator. Thanks.

9. Assume that you expect to hold a $20,000 investment for one year. It is forecasted to have a year end value of $21,000 with a 30% probability; a year end value of $24,000 with a 45% probability; and a year end value of $30,000 with a 25% probability. What is the standard deviation of the holding period return for this investment? A) 12.1% B) 14.4% C) 16.86% D) 33.5% Answer: C