Resonance frequency of beam (calculation+plot)

HI

I want to calculate and plot resonance frequency of cantilever that I designed in MEMS module. Based on the previous discussions here I understand that I should do the study in "Eigenfrequency" and then i can get different modes of resonance frequency, is that right?
I did what I have mentioned above, and I got 6 eigenfrequency. However there are two problems.

1- I can not understand what equation comsol is using for calculating this resonance frequency. For mu theoretical calculation of first mode of resonance frequency I used this formula "f=0.162(t/L^2)squrt(E/Rho)
by using this equation I get resonance frequency of 95 K, but the simulations give me first eigenfrequency of 117K. Is this differences normal?

2-I can not plot find out how I can plot frequency vs. amplitude to have a simple resonance frequency plot with a pick on resonance frequency.

I would be grateful if someone can help me with this.

Regards
Bahar