Hello, thank you for taking the time to post your question!
Since you are just selecting one piece of candy you can go ahead and add together all of the different options.
That means taking
8 + 6 + 4 = 18
So there are 18 different ways to select one piece of candy
I hope that helps you get moving in a better direction on this type of question! Feel free to reach out if you have any additional questions beyond that :)