Explanation:
X component = 4.5 - 2.1 = 2.4
Y component = 7.8 - 2.1 = 5.7
Find magnitude using Pythagorean theorem
m^2 = 2.4^2 + 5.7^2
magnitude = 6.18 units
Remember for a right triangle tangent Φ = opposite leg / adjacent leg
angle = arctan ( 5.7 / 2.4 ) = 67.2 degrees