You are currently converting Distance and Length units from Centimeters to Feet 321 Centimeters (cm) = 10.5315 Feet (ft) This is a hard one but see if this helps if not let me now and i can try again..
You are correct...amplitude will be the answer
The formula v=fλ can be used here.
326=2500*λ
Note the 2500 as 2.5kHz is 2.5 thousand Hz.
λ = 326/2500
= 0.1304m = 0.130m
