It may be needed that you want to type multiple lines of text a particular cell. The main concern lies in the fact that under Excel when you press the Enter Key, the cursor will move to the next cell.

You can subtract multiple cells from one cell in Excel by using Minus sign, SUM function and Paste Special feature. Here is a tutorial on this.

You can sum cells across multiple sheets in Excel. This article presents steps for Adding single-cell values or Adding values in the range of cells.