need help please

The intensity L(x) of light x feet beneath the surface of the ocean satisfies the differential equation dL dx - = - KL. From experience, a diver knows that diving to 17 ft in a sea cuts the intensity in half. He cannot work without artificial light when the intensity falls below one-tenth of the surface value. About how deep can he expect to work without artificial light? He can work approximately ft deep without artificial light. (Simplify your answer. Round to the nearest tenth as needed.)