The displacement is 6.7 km to the northeast.
Displacement = 5 km + 1 km = 6 km to the east and 3 km to the north.
The net displacement is the hypotenuse of a right-angled triangle with sides
6 km and 3 km.
According to Pythagoras’ Theorem,
a^2 + b^2 = c^2, where c is the hypotenuse and a and b are the other two sides.
c^2 = (6 km)^2 + (3km)^2 = 36 km^2 + 9 km^2 = 45 km^2
c = √(45 km^2) = 6.7 km NE