Highest common factors...

Identify the highest common factor of 9 and 30.

$\begin{array}{lcll} \text{Factors of } 9 &:& 1, {\color{red}3}, 9 \\ \text{Factors of } 30 &:& 1, 2, {\color{red}3}, 5, 6, 10, 15, 30 \\ \end{array}$

$\begin{array}{rcll} 3 \text{ is the Greatest Common Factor } \end{array}$