NASA is getting ready for a spacewalk to do some repairs on the space station.Some of the equipment used for the walk, will require a supply of electricity they can take with them for ease of mobility.The current mobile power supply requires 2 batteries to function.If either of the batteries dies, the power supply will not function.When that happens, the crew must remove the failed battery, and replace it with a new replacement battery.

Currently, we have 2 new batteries in the power supply.

Each battery, after it is placed in the power supply, lasts a random number of hours that is distributed with a 35% chance of lasting 15 hours, 40% chance of lasting 18 hours, 25% chance of lasting 25 hours.

As an example: For the first two batteries, assume that Battery 1 will fail after 19 hours, and Battery 2 will fail after 20 hours.The power supply will fail after 19 hours, when Battery 1 is replaced and calculation for the time of failure of the new battery begins.

An hour later, Battery 2 fails and is replaced and calculation for the time of failure of the new battery begins. The power supply fails next when all replacement batteries fails first.

You need to help them decide how many spare batteries to take.Use simulation to estimate the amount of time the power supply can last with batteries currently available and any spare batteries they would take.Your choices for spare batteries are an extra 1, 2, 3, or 4 batteries (recall the power supply has 2 brand new batteries).The space walk missions are going to total around 55 hours, so the power supply needs to supply power for that long if possible.