Let the starting point be the origin with coordinates (0, 0).
Assume West corresponds to the negative x-direction and North corresponds to the positive y-direction.
Mr. X walks 70 m West:
Position: (-70, 0)
Turning left from West means facing South. He walks 35 m South:
Position: (-70, -35)
Turning left from South means facing East. He walks 30 m East:
Position: (-70 + 30, -35) = (-40, -35)
Turning left from East means facing North. He walks 35 m North:
Position: (-40, -35 + 35) = (-40, 0)
The distance from the starting point (0, 0) to the final position (-40, 0) is:
d=(0−(−40))2+(0−0)2
d=402+0
d=1600
d=40 m
Therefore, Mr. X is 40 m from the starting point.