How do you make a precise estimation of painting expenses for a Home Office in Bern with including ceilings, 2 doors, and 1 windows, covering an area of 9m x 6m?

Making a precise estimation of painting expenses for a Home Office in Bern, including ceilings, 2 doors, and 1 windows, covering an area of 9m x 6m, involves accurately calculating CHF 840.00.

*) The calculations are approximate, based on a room height of 2.4m, and include one coat of paint. The price covers only the labor, excluding any services or materials.