Frictionless Ramp and Graph Analysis

Please explain how to interpret the graph... because i could not interpret the graph i was unable to do the rest of the problem.

A dated box of dates, of mass 9.10 kg, is sent sliding up a frictionless ramp at an angle of θ to the horizontal. Figure 5-43 gives, as a function of time *t*, the component *vx* of the box's velocity along an *x* axis that extends directly up the ramp. What is the magnitude of the normal force on the box from the ramp?

http://edugen.wiley.com/edugen/cours...5/fig05_43.gif**Fig. 5-43**