Not very much sense! Sounds to me like you are memorizing formulas (poorly) without understanding what is being done.I want to know how you come about that sum and how I would apply it to other figures for example £45 VAT of 25%.
Hope my explanation makes sense.
What is "25% of 45£? (That is the same as 0.25 times 45£.) What do you get when you add that tax to 45£?