If you want your profit, £700, as percentage of your cost, £4,400, which is what it appears to be, then it is [tex]\frac{700}{4400}= 0.159[tex] or 15.9 %. Now multiplying 4,400 by that will NOT give you 5,100- it's not supposed to- it will give your profit: 700. Multiplying 4,400 by 1+ 15.9%= 1.159 will give your costplusprofit= selling price:

1.159(4,400)= 5099.6 (not exactly 5100 because 15.9% is rounded.)