The easiest way to do this is draw a diagram. Draw out a right triangle, and call each of the two bases one of the vectors. The hypoteneus is the magnitude in this case (since if you stack the vectors head to tail, you get this right triangle). Remember that formula,
[tex] \sqrt{ {a}^{2} + {b}^{2} } [/tex]
Where a and b are each of the sides with 100 km/hr.
If
[tex] \sqrt{ {100}^{2} + {100}^{2} } = 10 \sqrt{2} = 141[/tex]
ANSWER: 141 km/hr
