A quarter note is typically worth 1 beat in four-four time. When a dot is added to a note, it increases the duration of the note by half of its original value.
So, the dot adds half of a quarter note's value (which is 0.5 beats).
Therefore, a quarter note with a dot is worth: 1 beat (for the quarter note) + 0.5 beats (for the dot) = 1.5 beats.
The correct answer is:
C. one-and-a-half beats