What percentage of customers don't call after using webchat

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Hope someone can help!

• I need to look at all contacts that have ever used a chat (so the source if webchat) - this is fine
• I then need to see out of those, how many called up (this is determined by the subject of the request which is "TELEPHONE CALL")
• This will then lead me to a conclusion to say that out of everyone that used webchat for the first time, X% used the phone afterwards (instead of continuing to use webchat)

This is just a rough figure we need and nothing concrete. We want to push people to use webchat rather than the phone and hope this is someone that we can produce