A brand of cereal had 1. 21. 21, point, 2 milligrams (\text{mg})(mg)left parenthesis, start text, m, g, end text, right parenthesis of iron per serving. Then they changed their recipe so they had 1. 8\,\text{mg}1. 8mg1, point, 8, start text, m, g, end text of iron per serving. What was the percent increase in iron?.