An easier way is to add V.A.T is to multiply :- X*1.Y where X is the amount to add V.A.T to and 1.Y is the V.A.T rate eg £74.59p + V.A.T. @17.5% ( 74.59* 1.175) = £87.64p.
To subtract V.A.T divide :- X/1.Y where X is the amount to remove V.A.T from and 1.Y is the V.A.T rate eg £87.64 - V.A T @ 17.5% (87.64/1.175) = £74.59.
To find amount of V.A.T subtract :- 87.64 - 74.59 = 13.05 therefore V.A.T on £74.59 is £13.05p.