I need some help in math also please explain how you got the answer

What is the measure of ac? 5 units 13 units 26 units 39 units 3x- 2b 6x + 9

Which best explains why this triangle is or is not a right triangle ?

1. why is a frequency distribution useful? it allows researchers to see the "shape" of the data. it tells researchers how often the mean occurs in a set of data. it can visually identify the mean. it ignores outliers. 2. the is defined by its mean and standard deviation alone. normal distribution frequency distribution median distribution marginal distribution 3. approximately % of the data in a given sample falls within three standard deviations of the mean if it is normally distributed. 95 68 34 99 4. a data set is said to be if the mean of the data is greater than the median of the data. normally distributed frequency distributed right-skewed left-skewed