What is the formula used to calculate the number of image formed by multiple reflection ?

Question

$\begin{array}{1 1} (a)\;\text{ $\frac{360^{\circ}}{angle\; between\; mirror}$} \\ (b)\; \text{($\frac{360^{\circ}}{angle\;between\; mirror})+1$} \\ (c)\; \text{($\frac{360^{\circ}}{angle\; between \;mirror})-1$} \\ (d)\; \text{$\frac{angle \;between \;mirror}{360^{\circ}}$} \end{array}$