Answer
$R=k\left(\frac{L_1}{r_1^4}+\frac{L_2}{r_2^4}\right)$
Work Step by Step
$$R=R_{1}+R_{2}$$
Using the results of the pervious exercises it follows:
$$R=k\cdot \dfrac{L_1}{r_1^4}+k\cdot \dfrac{L_2}{r_2^4}=k\left(\dfrac{L_1}{r_1^4}+\dfrac{L_2}{r_2^4}\right)$$
