I've never had to perform multiple regression through Excel before so forgive
any simple mistakes or assumptions.

I'm trying to create a relationship between 3 variables (Crossfall, gradient
and flow width) and an output (Area). Having arranged the data in a suitable
way that Regression Analysis could be carried out I'm presented with 3
variables. However, nowhere does is specify what in format these variables
are applied / combined such that I may produce a result.

Is it a simple y=Aa+Bb+Cc+I? Or is there something more complex? I have
tried with the above format but the equation does not reproduce the figures
that I'm after.

Cheers,

RickH