If stock is sold three months after it is purchased, the formula above relates p, d, s, and r, where p is the purchase price of the stock, d is the amount of any dividend received, s is the selling price of the stock, and r is the yield of the investment as a percent.If Rose purchased $400 worth of stock received a $5 dividend and sold the stock for $420, for three months after purchasing it, what was the yield of her investment, according to the formula?(Assuming she paid no commissions.)