Answer
$\cos(\theta)=\frac{1}{256}$
$\theta=\arccos\left(\frac{1}{256}\right) \approx 90^{\circ}$
Work Step by Step
From the previous part it follows:
$$\cos(\theta)=\frac{r_2^{4}}{r_1^{4}}$$
$$\cos(\theta)=\frac{(\frac{1}{4})^{4}}{1^{4}}$$
$$\cos(\theta)=\frac{1}{256}$$
$$\theta=\arccos\left(\frac{1}{256}\right) \approx 90^{\circ}$$
