Wavelength and Frequency with Temperature

[yoshiba]

Homework Statement

Two loudspeakers are 2.5 m apart. A person stands 2.9 m from one speaker and 4.0 m from the other. Assume the air temperature is 20°C.
a) What is the lowest frequency at which destructive interference will occur at this point?

(b) Calculate the next two frequencies that also result in destructive interference at this point.

Homework Equations

not sure if these apply:
v=f*lambda
L=n(lambda/2)
L=n(lambda/4)

The Attempt at a Solution

i have no idea how to get a start on this problem

 

[Kurdt]

What do you know about destructive interference?

 

[yoshiba]

I think i figured it out:
for destructive interference, one difference in distances is half of the wavelength.
so 4-2.9=1.1
1.1=.5(lambda)
2.2=lambda
then i use the equation with temperature, solve for the temperature at 20 degrees C
and plug wavelength and velocity in the v=f*(lambda) equation.
right?

 

[Redbelly98]

Yes.

For the rest of the problem, what other values can the difference in distances have?

p.s. don't forget to show units consistently throughout your solution.