It takes the son one and half hours to clean the house. To find this you need the equations F+S=2 and F+1=S. (F=father and S=son) You take the F+1 and substitute it in for S in F+S to get F+(F+1)=2. Then you combined like factors, 2F+1=2, and simplify to get F=.5hr. After this you plug .5 in to F+1=S to get (.5)+1=S, meaning it takes the son 1.5 hour to clean the house.
TO find perimeter you add all sides. But to find the totaly of each side, you will divide. So a triangle has 3 sides, so you divide 45 by 3 to get the sides length of: 15 cm each ~hope this helped :)
