Modifying Volumes in X/Y/Z Directions

I am looking to manipulate volumes in Rhino in the X, Y, and Z directions with Grasshopper. I am using Box Rectangle to change the height, but am not sure how to change length and width simultaneously. I am new to the software, and not sure what components to use. Thank you!

Or to center the box, construct a domain with expressions “-x/2” on the ‘A’ input and “x/2” on the ‘B’ input:

Thank you!! Would you know how to also attach this definition to an existing rectangle I have drawn in Rhino?

You need to find a beginner’s tutorial.