Rx - st = r
Rx = r + st Add st to both sides
Rx - r = st Subtract r from both sides
(Rx - r)/t = s Divide t on both sides ( to isolate s)
[tex]rx-st=r\qquad\text{subtract rx from both sides}\\\\-st=-rx+r\qquad\text{change the signs}\\\\st=rx-r\qquad\text{divide both sides by}\ t\neq0\\\\\boxed{s=\dfrac{rx-r}{t}}[/tex]
