(1) The apprentice paints x square meters every day, and the room area is y square meters.

3*(X+30)=8Y-40

5*X=9Y

X=90 Y=50。

The wall area to be painted in each room is 50 square meters.

(2)36*50/(90+30+90*2)=6 (days)

(3) Wages are paid on a daily basis.