Question 624052
{{{S=L(1-r)}}}


{{{S=L-Lr}}}


{{{S-L=-Lr}}}


{{{-Lr=S-L}}}


{{{Lr=-(S-L)}}}


{{{Lr=-S+L}}}


{{{Lr=L-S}}}


{{{r=(L-S)/L}}}


So the solution is {{{r=(L-S)/L}}}