Can anyone check this math problem for me its Proofs Geomotery

Which values for a and b will create infinitely many solutions for this system of equations? ax-y=8 2x+y=b

What is the order of magnitude for the number of liters in a large bottle of soda served at a party

You were told that the amount of time lapsed between consecutive trades on the new york stock exchange followed a normal distribution with a mean of 15 seconds. you were also told that the probability that the time lapsed between two consecutive trades to fall between 16 to 17 seconds was 13%. the probability that the time lapsed between two consecutive trades would fall below 13 seconds was 7%. what is the probability that the time lapsed between two consecutive trades will be between 14 and 15 seconds?