How do I solve this on a HP$10$bII$+$ Financial Calculator:

Consider the following returns and states of the economy for TZ$.$Com.:

Economy Probability Return

Weak $40\%2\%$

Normal $50\%10\%$

Strong $10\%37\%$

What is the standard deviation of TZ$\text{'}$s returns? SET YOUR CALCULATOR TO FOUR DECIMAL PLACES AND ROUND TO $2$ DECIMAL PLACES AT THE END. DO NOT ENTER THE $\%.$ FOR EXAMPLE, IF YOUR ANSWER IS $7\mathrm{.}7011\%$ ENTER IT AS $7\mathrm{.}70.$