Answer:
200m
Step-by-step explanation:
The contour interval on this map is 50m, which means each line moving in from the outer lines to the center increases by 50m in elevation. Line "A" can be discerned to be at an elevation of 650m based on its location from 550m. Line B is at 850m compared to the 800m line. This is a change of 200m (850-650 = 200).