Let the starting position be at the origin with coordinates (0,0).
Alisha goes 30 meters North:
Position: (0,30)
Turns right (now facing East) and walks 40 meters:
Position: (40,30)
Turns right again (now facing South) and walks 20 meters:
Position: (40,10)
Turns right again (now facing West) and walks 40 meters:
Position: (0,10)
The distance from the original position (0,0) to the final position (0,10) is:
d=(0−0)2+(10−0)2
d=0+100
d=100
d=10
Therefore, Alisha is 10 meters from her original position.