Please can someone help mi with this physics question? please I need the help.

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.)

See the attachment and solve question 5th

What is the name of the perceived change in a sound wave’s frequency due to motion between the observer and the sound source?