Select checkbox menu item → → to make the table look like a spreadsheet.

Click in cell E2 and use → → to insert a new formula at caret position.

The Formula Editor is displayed:

After sign '=', type `A2*D2`

and then click OK (shortcut **Ctrl**+**Enter**).

You have inserted your first formula in the document. A formula is visually represented by a small F icon. Don't worry if you find it ugly: it will disappear when you'll print the document or when you'll convert it to other formats.

Click on the F icon. Notice that:

The node path bar displays: `/html/body/table/tbody/tr/td/#processing-instruction(xxe-formula)`

, which means that a formula is processing instruction `xxe-formula`

(more on this later).

A red line is drawn around the F icon, which means that you have explicitly selected this processing instruction.

The status bar displays: `=(A2*D2)`

. The small F icon is in fact a special purpose button (more on this later).

Copy the formula (**Ctrl**+**C**) to the clipboard and paste it (**Ctrl**+**V**) in cells E3 and E4.

Now type in cell A2: `2`

, tab to cell B2 to type: `xe-1u`

, tab again to cell D2 and type: `200`

. Do the same in the next two rows: `1`

,`xe-5u`

,`800`

and `1`

,`fc-uu`

,`3000`

. Then click in cell E5 to force an update. The table should now look like this:

### 1.1. Three more formulas to finish first version of the invoice

Click in cell E5 and insert formula: =sum(E2:E4)

Click in cell E6 and insert formula: =rounddown(E5 * left(D6, len(D6)-1)%, 2)

left(D6, len(D6)-1) is string "19.6%" without its last character '%'.

Note that you can use spaces in a formula and that a formula is case-insensitive. For example: SUM(e2:e4) works fine too.

Click in cell E7 and insert formula: =E5+E6