3. Which accidental is used in measure 15? How does this accidental alter the original note?

The accidental is a natural symbol, which changes the B flat note to a B natural note.

Ifound this on google “a skewed (non-symmetric) distribution is a distribution in which there is no such mirror-imaging. a "skewed right" distribution is one in which the tail is on the right side. a "skewed left" distribution is one in which the tail is on the left side. the above histogram is for a distribution that is skewed right.” i hope this you for what your looking for