How to make the spectrum of two spikes?

Hello everyone, I would appreciate if somebody direct me regarding the spectral analysis for spike trains as I am new in this field.

I have two spike trains , R1=0.2 and R2=o.7

I would like to plot the spectrum of the two and my instructor says the spectrum of a pair of spikes is a sinusoid. Any suggestions about how to write the code will be more than appreciated. Thank you.