Problems $8)$ and $9)$ depend on the circuit shown below.

The value of the resistor $R_2$ is

a$)4$

b$)2$

c$)8$

d$)6$

The power delivered by the $40$ V source is

a$)$ can't be found due to the unknowns $V_1$ and $R_1$

b$)240$ W

c$)400$ W

d$)160$ W