At the end of a snow storm, Caleb saw there was a lot of snow on his front lawn. The temperature increased and the snow began to melt at a steady rate. The depth of
snow on Caleb's lawn, in inches, can be modeled by the equation S = -2t + 18,
where t is the time, in hours, after the snow stopped falling. What is the y-intercept
of the equation and what is its interpretation in the context of the problem?