Question: rearring equations

Hi I know this is a simple question but i have completely forgotten how to do it: I have the following equation, 

h := ((A-B)^2*(A-4-B^2+4*B)*(A-4-B^2-4*B)-Q^2*(A-4-B^2+4*B))/(Q^2*(A-4-B^2-4*B))-1

how can I find what B is equal to?

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