need help

A cascade impactor is used to measure the particle distribution in a stream of air. Analysis shows that the distribution is log-normal with a dso of 7.0m and 9 of 2.0 . Assume that the particles have a unit density (1000kg/m3) and are spherical. (a) Plot the mass of the particle distribution against the size. (b) What is the percent of the mass in the distribution below the size of 2.0m