I'm not sure I get it, the x is acceleration and y is velocity? Might be easier to imagine two graphs, one for acceleration vs time, one for velocity vs time.
I think you would have to plugin 3 for t and solve for m/s and m/s^2, somehow. But m/s^3 is like double acceleration, I've never seen that before. Or I'm confused with something else...
That's always the problem with questions that rely on being able to answer the preceding. Being able to get the magnitude you need to do the complex math beforehand. Lol, I would've skipped that question as soon as I've seen it...