The 3 cm vector represents 63 km.
Since a 1 cm long vector represents a displacement of 21 km, we need to find the number of kilometers a 3 cm vector represents.
Let x represent the displacement the 3 cm vector represents.
By ratio, we have 1 cm: 21 km = 3 cm : x
So, 1 cm/21 km = 3 cm/x
Cross-multiplying, we have
x × 1 cm = 3 cm × 21 km
x = 3 cm × 21 km/1 cm
x = 63 km
So, the 3 cm vector represents a displacement of 63 km.
Learn more about displacement here:
brainly.com/question/17673000