Let's use algebra and solve for k.
[tex]8k+2m=3m+k\\8k-k=3m-2m[/tex] (putting k on one side and m on another)
[tex]7k=m\\k=\frac{m}{7}[/tex]
This is the final answer.
ANSWER: [tex]k=\frac{m}{7}[/tex]