This is a very simple problem.
Firstly, you are told the current through one of the resistors in series is 240mA. This is the current though all the resistors because they are in series. By Ohms law, the total resistance will be 240/.240 = 1,000 ohms.
The third resistor is 208 ohms and the current flowing though it is .24A This means the voltage across it is .24 x 208 = 50v
The voltage across the first resistor is 240 - 110 - 50 = 80v
The resistance of R1 = 333R
The resistance of the second resistor = 1,000 - 208 - 333 = 459R