Calculating current in one branch of circuit
You need to use superposition to solve this circuit.  

Superposition means solve for the current i due to the voltage source, with the current source set to 0A (i.e. current source disconnected).  Then, find the current i due to the current source, with the voltage source set to 0V (i.e. voltage source shorted).  Then, add the two together to get the final answer.  Good luck!