The intensity of light I at time t hours after sunrise and at a depth of x feet below the ocean surface
is given by I(x,t) =Ioe–kx sin3t
D , where D is the length of daylight in hours, Io is the intensity of
light on the surface of the water at midday, and k is a positive constant. Assume D = 14, Io= 50,
and k =0.006. In a study of the effect of light on ocean plants, a scientist needs to determine the
minimum depth x at which a plant would never at any time be exposed to an intensity of light
greater than 25. What is this minimum depth?