Now, before we continue, I want to stress the importance of what dy/dt and dx/dt actually mean.
When we're dealing with time, space, and movement along a one-directional plane, we're moving with two scalar quantities (using our parametric representation of a particle), namely its x-direction and its y-direction.
Thus, by differentiating x with respect to t, we're literally saying: "well, what is the change of rate of x in relation to time", or "as t moves along the plane, what is the change of rate of x in that time?"
This can be stressed for the y-ordinate, as well.
So, the change of rate of the y-ordinate (dy/dt is 4cm/s). This is how fast the vertical quantity is changing as time changes at that point.
I would go with answer D here just because it is the only option over 13, and the hypotenuse is always larger than the other sides. Im not positive on the math behind it though tbh.