A student is jogging on a straight path with the speed $5.4 \mathrm{km}$ per hour. Perpendicular to the path is kept a pipe with its opening $8 \mathrm{m}$ from the road (see figure). Diameter of the pipe is $0.45 \mathrm{m}$ At the other end of the pipe is a speaker emitting sound of $1280 \mathrm{Hz}$ towards the opening of the pipes. As the student passes in front of the pipe, she hears the speaker sound for $T$ seconds. $T$ is in the range (take speed of sound, $320 {\mathrm{ms}}^{-1}$):

• Correct answer
  A

  $6-12$
• B

  $12-18$
• C

  $3-6$
• D

  $18-22$

Hence, the correct answer is option: 'A'.