To create a visual separation between two sections you use white space. This becomes a white bar when you print.
You will find this option under the '+ Other' button, next to the other options for adding a line or a line of text.

You provide the tag [ITEM_WITHOLD] in a separate row in the calculation table. You can then style this row via CSS to determine its own size. You can find more information about the calculation table in this help desk article.