Solve for indicated variable? HELP!!!!!?

Question

Solve the question for the indicated variable.

I=nE/nr+R ; solve for n.

Generally I am excellent on these problems but this one has me stumped. Please help!

Answer 1

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l = nE/(nr+R)

=> lnr + lR = nE

=> n(E-lr) = IR

=> n = IR/(E-lr)