Annabelle is taking the polar express all the way to the north pole! the polar express is 100 meters long and it takes 30 seconds to cross santa’s 400m ice bridge. what speed is the train going at? (30,45,60,80km/h)

When a vertical beam of light passes through a transparent medium, the rate at which its intensity i decreases is proportional to i(t), where t represents the thickness of the medium (in feet). in clear seawater, the intensity 3 feet below the surface is 25% of the initial intensity i0 of the incident beam. what is the intensity of the beam "10" feet below the surface? (give your answer in terms of i0. round any constants or coefficients to five decimal places.)