Point W is somewhere on segment UV. UW = 18 and WV = 21 Find UV

Answer 1

A line segment has 2 endpoints - in this case point U and point V. We are told there's a third point W on this segment, and since U and V are the endpoints, then W is in-between. If we drew a diagram it'd look something like this:

U ----- W ----- V

Question states that the line portion from U to W is 18, and the portion from W to V is 21. Visually we can see that the section from U to W and the section from W to V together combines to make the bigger line segment UV.

UV = UW + WV

UV = 18 + 21

UV = 39

Answer 2

UV = UW + WV = 39