My class has just started Multivariable, and I'd just gotten back my quiz results. However, I don't understand why for B), the correct graph is apparently in the other direction I thought it would be — from what I see from the graph of $f(x,y)$, shouldn't how I drew it be right (according to the axes labels I drew)? Any help would really be appreciated!
Also, I'm sorry for the second image. I'm not sure how to rotate it to put it right...
Your solution seems correct, indeed from the 3D plot we can see that for $y=1$ we have that $z$ is strictly decreasing with $x$ increasing. To better visualize, the plot in the $x-z$ plane for $y=1$ is similar to $z=-x^3$.