PLEASE SHOW STEP BY STEP FORMULAS WITHOUT EXCEL ONLY CALCULATOR

There is a probability of 0.47 that there will be extremely cold weather this coming Winter. If it does, we expect investors of Star & Bucks to achieve a return of 0.19. Else, investors may expect a lower return of 0.06. Can you estimate the standard deviation for investors of Star & Bucks? Type your answer as decimal (i.e. 0.052 and not 5.2%). Round your answer to the nearest four decimals if needed