Simplifying Rs = st + -1Rt Solving sR = st + -1tR Solving for variable 's'. Move all terms containing s to the left, all other terms to the right. Add '-1st' to each side of the equation. sR + -1st = st + -1st + -1tR Combine like terms: st + -1st = 0 sR + -1st = 0 + -1tR sR + -1st = -1tR Combine like terms: -1tR + tR = 0 sR + -1st + tR = 0