Please help, thank you.

An arc subtends a central angle measuring 7pi/4 radians what fraction of the circumference is this arc?

Suppose medical records indicate that the length of newborn babies (in inches) is normally distributed with a mean of 20 and a standard deviation of 2.6. find the probability that a given infant is between 14.8 and 25.2 inches long.

I'm stumped by this question. someone with my math homework