Both of these verbs are used for asking about something or looking for information. The nouns for the request / investigation are enquiry and inquiry.
Technically, enquire is used for "ask" in general ("He enquired about prices for the products"), and inquire for a more formal investigation ("The police will make an inquiry into the alleged corruption.")
However, in American English it is now very common to use inquire for everything: "He inquired about prices for the products."
For a foul to result from failure to legally strike a rail after contacting a frozen ball, the ball in question must be inspected and designated as frozen prior to a players shot, otherwise the ball is not considered frozen. If the cue ball becomes wedged between an object ball and the cushion and frozen to both, then legal shot requirements must be met by pocketing the frozen ball, or by contacting either another ball or another cushion enroute to a legal shot. Failure to do so is a foul.