I have two math questions I need help on?

Question

Here is the first one: Simplify: m+m

And here is the next one: 9 km= how many meters?

Thanks so much. And please explain.

Answer 1

If you have one apple and add one apple, what do you get?  m + m = 2m

kilo means 1000, so 9 km = 9 (1000 m) = 9000 m