posted by vera .
lines AB and CD intersect at point E. Ray EF is perpendicular to line AB. What is the measure of <CEF?
No idea. Could be anywhere from 0 to 180 degrees.
You haven't said which side of the line AB points C and F are, or anything about any other angles. All we know is that EF and AB are perpendicular. Point C could be anywhere except A or B.