If Two Adjacent Frequencies of an Organ Pipe Closed at One

If two adjacent frequencies of an organ pipe closed at one end are 510 Hz and 635 Hz,what is the length of the organ pipe? (v_sound = 340 m/s)

A) 0.7 m
B) 0.9 m
C) 1.2 m
D) 1.4 m
E) ​2.7 m