Going crazy before finals... a little help would be greatly appreciated. Here are a few questions that I am having trouble with:

10. Consider the following two-step process. Heat is allowed to flow out of an ideal gas at constant volume so that its pressure drops from 2.2 to 1.4 atmospheres (=220,000 to 140,000 Pascals). Then the gas expands at constant pressure, from a volume of 6.8 to 9.3 liters (=0.0068 to 0.0093 cubic meters), where the temperature reaches its original value. Calculate a) the total work done by the gas in the two-step process, b) the change in internal energy of the gas in the two-step process, and c) the total heat flow into or out of the gas.

27. A nuclear power plant operates at 75% of its maximum theoretical (Carnot) efficiency between temperature reservoirs at 625 and 350 degrees Celsius. If the plant produces electrical energy at the rate of 1.3 gigawatts, how much exhaust heat is discharged per hour?

51. An inventor has designed and built an engine, which he says produces 1.50 megawatts of usable work while taking in 3.00 megawatts of thermal energy at 425 Kelvins, and rejecting 1.50 megawatts of thermal energy at 215 Kelvins. Is there anything fishy about his claim?

Thank you guys.