Here is a video to help you with concentration calculations. In Chemistry, concentration is know as molarity (i.e. the amount per volume).

Note that in the video, the lovely Tyler de Witt uses the unit “liter” for volume, but the correct international unit (as used by UK exam boards) is decimeters cubed (dm3) which is the same thing as Tyler’s “liter”.

and a follow up video with some more examples: