Two blocks sliding on top of each other

[pharoh123]

A 4 kg block is placed on top of a 8kg block, placed on a table with no friction,which is subject to force of 30N. What is the coefficient of friction needed between the two blocks so that the the top doesn't slide on the other one?

What i did was find the acceleration of the bottom block and then i found the force needed to push the top block at that acceleration. I considered that force the friction and found the coefficient. However, I don't think i got it right since i thought friction couldn't actually move an object and is only a resistance. So did i get right or not?
Thanks

 

[Redbelly98]

Welcome to PF

did i get right or not?

If you show your work, we can tell you. At the very least post your answer, but showing the entire work is better.