s=14
Explanation
[tex]\frac{2}{3}s+\frac{5}{6}s=21[/tex]Step 1
remember how to sum fraction numbers
[tex]\frac{a}{b}+\frac{c}{d}=\frac{ad+bc}{bd}[/tex]factorize s and sum the fraction numbers
[tex]\begin{gathered} \frac{2}{3}s+\frac{5}{6}s=21 \\ s(\frac{2}{3}+\frac{5}{6})=21 \\ s(\frac{12+15}{18})=21 \\ s(\frac{27}{18})=21 \\ s(\frac{3}{2})=21 \\ \frac{3}{2}s=21 \end{gathered}[/tex]Step 2
multiply both sides by 2/3
[tex]\begin{gathered} \frac{3}{2}s=21 \\ \frac{3}{2}s\cdot\frac{2}{3}=21\cdot\frac{2}{3} \\ \frac{6}{6}s=\frac{42}{3} \\ \\ s=14 \end{gathered}[/tex]so, the answer is s= 14
