To solve the equation, you must isolate s, which means to get it alone on one side. Since you are multiplying s by 21, you must divide by 21 to get s alone. However, whatever you do to one side of the equation you must do to the other, so if you divide both sides by 21 and simplify it will give you s.
\(21s=3 \\ \\ s= \frac{3}{21} \\ \\ s= \frac{1}{7}\)
