First off draw the circuit. The voltage across each resistor is equal (i.e. 6V). From here we just have to use Ohm's law (V = I x R) to calculate the currents across each resistor. This gives us:
R1; 6V = I x 3 Ohms; I = 2A
R1; 6V = I x 4 Ohms; I = 1.5A
R1; 6V = I x 5 Ohms; I = 1.2A