Find the number of possible natural oscillations of air column in a pipe whose frequencies lie below

Question:

Find the number of possible natural oscillations of air column in a pipe whose frequencies lie below vo = 1250 Hz. The length of the pipe is l = 85 cm. The velocity of sound is v = 340 m/s. Consider the two cases:
(a) The pipe is closed from one end;
(b) The pipe is opened from both ends. The open ends of the pipe are assumed to be the antinodes of displacement.