For part B, there are at least 2 methods of finding the current. The first method is to find the total resistance of the circuit. The second method is to find the current in 3R and 4R resistors respectively and then sum them up.
For part B, use part A answer to find the voltage across the R resistor. Then use the power formula V^2/R to find the power dissipated in the R resistor.
try redrawing the circuit so that there are two branches (one branch only containing the 3R resistor, and the other branch containing 2 1R, and 1 3R in parallel with the 4R being in series with them) As the voltage across the two branches is the same, to find the potential difference across the 4R resistor, you use the potential divider equation to find out the voltage across the 4R resistor.