What is the greatest common factor of 13 and 39 please help quick

The mean of a set of data is -3.82 and its standard deviation is 2.31. find the z score for a value of 3.99.

Sanya noticed that the temperature was falling at a steady rate of 1.4 degrees every hour from the time that she first checked her outdoor thermometer. by 6 a.m., the temperature had fallen 21 degrees. which expression can you use to find how many hours earlier she had first checked the thermometer?

What value is a discontinuity of x squared plus 8 x plus 4, all over x squared minus x minus 6?