Find angle $\theta$ if the following information is known Find $\color{green}\theta$
$\color{blue}{R_b}$ is the radius of the big circle
$R_s$ is the radius of the small circle
$\color{red}{d}$ is known
$x$ is known and is an angle


Hint (Sorry for the awful drawing): Parallelity, because otherwise there are infinitely many angles that are possible, then use the law of sines 
$$\dfrac{\sin\bar{\theta}}{R_b}=\dfrac{\sin x}{d}$$
to calculate the angle $\bar{\theta}$, then $\theta= 180°-\bar{\theta}$
