The area drawn by three first-class technicians every day = 8x -50, and the area drawn by one first-class technician every day = (8x-50)/3.

The area drawn by five secondary technicians in one day is = 10x +40, and the area drawn by one secondary technician in one day is = (10x+40)/5.

Each first-class mechanic paints more walls of 10 square meter than the second-class mechanic, so

(8x-50)/3-( 10x+40)/5 = 10

The solution is x=52 square meters.