Help on this Physics problem

[LuizH]

So it's not that hard but I can't make mistakes on this one because it's for extra points.

What I've assume is that the limit for the trailer not to pull up is that the reaction Ry at C is 0
then I've made Moment at point C, since I've moved the reference from G to C, m*ax creates a moment there too.
then I've found everything.
My calcs are here


Thanks for reading it!