An undergraduate business student has purchased a laptop computer for use during exams. This laptop is perfectly reliable except for two parts: its microchip, which has a MTBF = 15 hours and its battery, which has a MTBF =20 hours. Assuming that a new battery has just been installed and the student brings one spare, fully charged battery with him, what is the probability that the LAPTOP will perform reliably during a 3 hour exam