To calculate the % yield, you need to determine the actual yield of the reaction and compare it to the theoretical yield. The actual yield is the amount of product that is actually produced during the reaction, while the theoretical yield is the maximum amount of product that could be produced based on the amounts of reactants used.
In this case, the theoretical yield is 87,000 milligrams of iron, since this is the amount of product that was actually produced. The % yield is calculated by dividing the actual yield by the theoretical yield and multiplying by 100%.
Since the actual yield and the theoretical yield are the same in this case, the % yield is 100%. This means that the reaction had a perfect yield, with all of the reactants being converted into product.