How to get lengths of similar figured and scale drawing

Which expression can be used to determine the slope of the line that passes through the points -6, three and one, -9

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?

Which of the following pair(s) of circles have las a common external tangent? select all that apply. a and b a and c b and c