How to substitute an equation in an expression in WxMaxima?

Question

I am sorry but I am quite new to Maxima.I have the following expression

Expression

And i was trying to set maxima to rearrange it with this

Substitution

My aim is for maxima to remove Vout and Vin completely in order to have a final expression with just VCR.

I did it "by hand" by dividing numerator and denominator by Vin^2. The result I got and that I wanted maxima to do it by himself was:

Expected Output