Answer
2 in
Work Step by Step
We know that the length of the arc $s$ cut off by $\theta$ can be calculated as $s=r\theta$. Therefore, we also know that $r=\frac{s}{\theta}$.
We are given that $\theta=5.1$ and $s=10.2$ in.
Therefore, $r=\frac{10.2}{5.1}=\frac{10.2\div5.1}{5.1\div5.1}=\frac{2}{1}=2$ in.