How do you find the friction between 2 objects given that the acceleration of the objext is 8.75m/s²,7Newtons and o.8kg. The first object wi

Not clear to me either.  The arrangement of the two objects isn't specified (Is one on top of the other?  If so, which is which?); what does the 2-4 represent (no units are given); where are the forces applied?

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@ ALAN, maybe this one is for you.    

I don't even understand what it means.  

Thanks Alan