Final answer:
Ryan's order will be executed at $18.20 or better.
Step-by-step explanation:
When Ryan places a good-'til-canceled limit order to sell 300 shares of KM at $18 a share and the order reaches the trading floor, the order will be executed at $18.20 or better. This means that Ryan's order will be fulfilled at the best available price, which in this case is $18.20, or a higher price if it is available. Therefore, the correct statement is A) His order will be executed at $18.20 or better.