Before the new kids the ratio of girls to boys is 15:12 because there are 15 girls and 12 boys now you can simplify by dividing 15 by 3 and 12 by 3 to get 5:4 as your simplified ratio. As far as after the new kids. Since there is 1 new girl you do 15+1 to get 16 and there are 3 new boys so you do 12+3 to get 15 now 16:15 is already in simplest form so your answer is:
Before: 15:12 simplified as 5:4
After 16:15
Diagonally
the top of the closet
the volume of cuboid is given by length*breadth*height
the volume of above cuboid is 6*12*125=864cubic in.
volume of below cuboid is 18*10*8=1440 cubic in.
totoal volume = 1440+864l=2304 cubic in.