$${\mathtt{s}} = \left({\frac{{\mathtt{a}}}{\left({\mathtt{1}}{\mathtt{\,-\,}}{\mathtt{k}}\right)}}{\mathtt{\,-\,}}{\mathtt{a}}\right)$$
Solve for a
Thank you!
$$s=a(\frac{1}{1-k}-1)\\\\ s=a(\frac{1-(1-k)}{1-k})\\\\ s=\frac{ak}{1-k}\\\\ \frac{(1-k)s}{k}=a$$
+154 
