Question 904529
{{{1/R = 1/S + 1/T}}}
Move all non-S terms to one side.
{{{1/S= 1/R - 1/T}}}
Take the reciprocal of both sides.
{{{S=1/(1/R-1/T)}}}
Multiply numerator and denominator of the right hand side by {{{RT}}}.
{{{S=RT/(RT(1/R-1/T))}}}
{{{highlight_green(S=RT/(T-R))}}}