It is important to read the question very carefully. The trick lies in the way the question is written. Once it is understood, then the problem is easy. Number of persons required to rearrange the floor plans in 1 hour = 42 Number of persons required to rearrange the floor plans in 9 hours = 42 * 9 = 378 hours So it will take 378 hours by 9 persons to rearrange the floor. I hope this is the answer you were looking for and the procedure is also clear to you. Once you understand the procedure, you can attempt such problems on your own in future.
A right angle means that the lines will create an L or X or T when they intersect. This is exactly the definition of perpendicular, that the shapes will intersect and create at least one right angle.
