Hi there!
[tex]3 {a}^{2} - 6a \: = 3a(a - 2)[/tex]
We can see this by writing the factors as multipliers. We get the following:
[tex]3a {}^{2} = 3 \times \: a \times a[/tex]
[tex]6a = 3 \times 2 \times a[/tex]
Now we can see that the terms that are in common are 3 and a, and therefore we can bring those outside the parenthesis.
