Hi, I need help with another question!

A microwave transmitter emits waves towards a metal plate. The waves strike the plate and are reflected back along their path.

I really wish I could put the diagram here but I don't think that's possible... The diagram shows 5 nodes (TSRQP), where minima of intensity is observed. These points are 15 mm apart. What is the frequency of the microwave?

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Answer is 10GHz but I got 6.7GHz :C

What I did:
I assumed that frequency is for the 4th harmonic. So, I did: F=(2*15)/4.5

How do I do this?

2 answers

wavelength=2(15mm)=.03m

freq=3E8/3E-2=10ghz
Thank you!!! :D