In a sale, an item is reduced by 20% and as a result makes only a 4% profit on the cost to the shop-keeper.
What percentage profit would the shop-keeper have
made if the item had sold at full price?

It would be the first choice, x^2+14x+49=16 because you can take out the square root on both sides of the equation whereas for the other options you would need to use the quadratic formula to solve them. Taking the square root is: (x+7)^2 = 16 which equals x+7=4...