A string fixed at both ends is $9\mathrm{.}20$ m long and has a mass of $0\mathrm{.}121$ kg$.$ It is subjected to a tension of $91\mathrm{.}0$ N and set oscillating.

$($a$)$ What is the speed of the waves on the string?

m$/$s

$($b$)$ What is the longest possible wavelength for a standing wave?

m

$($c$)$ Give the frequency of that wave.

Hz