Ok Betty, you have 2 tent, one is 40 cubic feet and the other is 75 cubic feet.
CFM needs are: you have to run at least 1 times your cubic feet per 3 minutes, but you have to consider temperature, humidity, carbon filter and CO2 if you inject and do it at saturation.
I made a topic espacelly for that and invite you to consult it…
So, for 40 cubic feet you’ll need 
40÷3= around 13.5 CFM
Add 5% for each lights you have, so, I presume that you have 2 lights fixtures so 10% more = 14.85 CFM, add 20% for your carbon filter = 17.82 CFM if you have temperature issues, add 25%, add 40 if you have also humidity issues, so, 22.28 CFM for heat issues and 24.95 CFM, so, 25 CFM should be enough for the smaller one (2×4×5)
You just need to apply this on the other one, but it should give you around 40-45 CFM,
These are absolute minimum.
I will let you choose your options or I let someone else guide you further.
~Al 
