At the end of a snow storm, Amelia saw there was a lot of snow on her front lawn. The temperature increased and the snow began to melt at a steady rate. After the storm, the snow started melting at a rate of 1.5 inches per hour and it is known that 4 hours after the storm ended, the depth of snow was down to 12 inches. Write an equation for S
,
S, in terms of
t
,
t, representing the depth of snow on Amelia's lawn, in inches,
t
t hours after the snow stopped falling.