Question 23592
Since you've given no clear question, I'm assuming we have y=3(t-s), and need to solve for s.  We need to get s alone, so we first expand the right side, and get y=3t-3s.  We now place all variables other than s on the opposite side, so y-3t=-3s.  To get only s, we divide all terms by -3 to get (-1/3)y + t = s, or
s=t-y/3.