Suppose that $x$ is the yield on a perpetual government bond that pays interest at the rate of $$\$ 1$$ per annum. Assume that $x$ is expressed with continuous compounding, that interest is paid continuously on the bond, and that $x$ follows the process.
$$
d x=a\left(x_0-x\right) d t+s x d z
$$
where $a, x_0$, and $s$ are positive constants, and $d z$ is a Wiener process. What is the process followed by the bond price? What is the expected instantaneous return (including interest and capital gains) to the holder of the bond?