Voltage Division Problem
I will help guide you to the solution.  Since the lightbulb draws 0.5A with 1.5 volts across it, you can use Ohms's law to calculate the resistance of the light bulb.  Now you have a voltage divider that must provide 1.5 volts when the light bulb is connected and 2 volts when it is not.  Those 2 conditions give you 2 equations for the 2 unknowns, R1 and R2. Use them to solve for R1 and R2.