The pressure P (in pounds per square foot), in a pipe varies over time. Five times an hour, the pressure oscillates from a low of 80 to a high of 280 and then back to a low of 80. The pressure at time t = 0 is 80. Let the function P = f(t) denote the pressure in pipe at time t minutes. Find a possible formula for the function P = f(t) described above.