Welcome to Autodesk Forums!

Hi @Anonymous 

Although I don't see "yellow plate" in the drawing you attached, I recreated it, well maybe something similar.

You can use Subobject selection technique to edit, move in your case, upper face of the plate.

Set UCS to World.

Press and hold Crtl key ob keyboard and click on upper face of the plate, you will see red dot - Subobject grip.

Now select this grip and move your mouse up, from keyboard entry distance - 2.7 and hit Return:

Upper face move 2.7 units up and you get 5.7 thickness (3.0+2.7=5.7)

For reference look >>>>here<<<<