We are given the following
[tex]k=am+3mx[/tex]we want to express m in terms of the other variables. So, what we will do is apply math operations on both sides, so we "isolate" the m variable on one side of the equation.
So, we begin by factoring the m on the right side, so we get
[tex]k=m\cdot(a+3x)[/tex]Now, we divide both sides by (a+3x). So we get
[tex]m=\frac{k}{(a+3x)}[/tex]which is our final answer.