to measure the distance from point C to point B, but the lesson did not go over how to accurately measure the distance- would I need a ruler for this?…

I am trying to figure out how to measure the distance from point C to point B, but the lesson did not go over how to accurately measure the distance- would I need a ruler for this? Also, I am assuming the scale with numbers at the bottom of the map can be used for this, but I’m unsure exactly how to figure the distance with what’s shown. Thank you!