Did you look at what I’d written in your other post, and try to understand it?
To expand on that what @Silver-Streak wrote,
This bit adds string together, or concatenates them :
VariableString(first)+VariableString(Second)+VariableString(Third)
This part converts the concatenated string into a number :
ToNumber(VariableString(first)+VariableString(Second)+VariableString(Third)
And the this final bit multiplies the last number with the result of the parsed concatenated variables :
ToNumber(VariableString(first)+VariableString(Second)+VariableString(Third))*Variable(forth)