a. Simple application of Ohm's law.
b. Voltage across the resistor is unchanged from part a. What is the new current?
c. Now current is unchanged from part a, but the voltage across the resistor is lower.
For each case, the current in the line can be determined from the delivered power and voltage.
(There were a lot of hints already given in the problem statement...)
How can you make an 8 ohm resistor from 10 ohm resistors? Since it is a lower value, there must be a parallel configuration involved...
Start by determining the maximum allowed temperature rise. The power associated with this temperature rise can be determined from 2.3 watts/degree.