Is possible get the percent of a word in the content of a richtexbox? if yes, can you give me some example?

For example if I have 100 words in a richtextbox and I want to know what is the percent of a word in this content (for example if a word called "music" is repeated 10 times = 10%. If this is not possible in a richtextbox, is possible in other box like textbox?

Sorry for my bad english.