# Reference framefrom masteringphysics

This is the only problem taht i could not figure out for 2 hours...
I even asked one of my friend who got 5 on his ap exam about this problem..he said no no to this question..anybody willin to help?

.Susan, driving north at 60 mph, and Shawn, driving east at 45 mph, are approaching an intersection

Q: What is Shawn's speed relative to Susan's reference frame?

$$\vec{v}_{(Shawn/Susan)} = \vec{v}_{(Shawn/Ground)} + \vec{v}_{(Ground/Susan)} = \vec{v}_{(Shawn/Ground)} - \vec{v}_{(Susan/Ground)}$$