I know for part a) the voltage is: (0.24A)(15) = 3.6V
and for part b) I did 6 / 4 = 1.5 A but this is wrong??
There's three (or four if you could consider the parallel component as one part) potential loops for this circuit. The equation for one going through the 4 ohm resistor and resistor R would be:
6 - 4I1 - RI2 = 0
Basically, find the single loop or path in the circuit that leaves I1 as the only remaining variable.