Hmm.....I don't know if it can be done the exact way you want it, and I don't know which cell is supposed to say "There are a x number of users in the room now!" but here's a sample.
Private Sub Worksheet_Calculate()
Dim r As Range
Dim r2 As Range
Set r = Range("B10")
Set r2 = Range("C10")
Application.EnableEvents = False
r.Offset(, 1).Value = "There are " & r.Value & " users in the room now!"
.Characters(InStr(r2.Value, r), Len(CStr(r))).Font.FontStyle = "Bold"
Application.EnableEvents = True
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