Taking x as the total number of teachers, we know that 30% of x is 21, it means that 0.3 times x is 21. We can use this information to find x, it means, the total number of teachers:
[tex]\begin{gathered} 0.3x=21 \\ x=\frac{21}{0.3} \\ x=70 \end{gathered}[/tex]
There are 70 teachers in the school.
