What is the mole fraction of h2s in the gas mixture of gases made up of 7.0 g of h2s, 10.0 g of ch4 and 12.0 g of o2

Iknow the answer to 13 is b and 14 is d. i just need to know why the correct answers are correct

Iknow the answer is a but i don't know why

Mike and mitchell decide to have a foot race. they mark off a stretch of 100 yards, and recruit cindy to work the stopwatch. after running the race and looking at the results, cindy declared that mitchell was the fastest. so how did the boys times compare?