Assuming that 'nivel' means nine, it will take the pair 36 minutes to clean their house.
If it takes one person 8 minutes to clean a room and the two work together the whole time, it'd be half of 8 for two people to clean a room, so 4 minutes.
With the nine(?) rooms, it'd be 4(9) [4x9] which would equal 36 minutes.
However, if it's not nine rooms, you'd still use the same idea of 8/2 = 4 and 4 times how many rooms there are.
