A chemist has two 2.0 g samples of zinc. Sample A consists of granules with a total surface area of 60 cm²; sample B is a powder with a total surface area of 300 cm². Both samples are separately reacted with excess 2.0 M HCl at 25 °C. Assuming the rate is directly proportional to the available surface area of the solid, by what factor should the initial rate for sample B differ from that for sample A? Give your answer as a numerical factor.