You can put this solution on YOUR website! In Math, when it says to "solve for" a variable, it means isolate that variable (i.e. get it by itself) on one side of the equation.
In your equation, s is just on one side of the equation but it is not by itself. We need to get rid of the extra term, 3t, and the "t" of "st". Once we have done that we will have "solved for s".
To make the 3t disappear we will subtract 3t from (or add -3t to) each side of the equation:
To make the "t" in "st" disappear, we will divide both sides by t:
The t's cancel on the left leaving:
We have solved for s! The above equation may be a sufficient answer. But we could simplify the right side a little by separating it into two fractions:
And the t's cancel in the last fraction giving:
(