Answer
(a) increase
(b) $618Hz$
Work Step by Step
(a) When the bottle is filled with helium, the fundamental frequency will increase as the sound speed increases and the length of the column is constant.
(b) We can find the new fundamental frequency as
$f_{He}=\frac{v_{He}}{4L}$
$f_{He}=\frac{3v_{air}}{4L}=3f_{air}$
We plug in the known values to obtain:
$f_{He}=3(260)=618Hz$
