How many combinations of 6 available out of 13 items?

This is different from the first one can someone me

The random variable x is the number of occurrences of an event over an interval of ten minutes. it can be assumed that the probability of an occurrence is the same in any two-time periods of an equal length. it is known that the mean number of occurrences in ten minutes is 5.3. the appropriate probability distribution for the random variable

Which expression gives you the distance between the points (5,1)and(9,-6)