Teacher c makes the most money at the end of their career since the model is entirely linear.
A:23,500 seats
B and C: both have 11,750 seats
C=x+9, c+x=99, c=99-x
So we have two equations equal to c, c=x+9 and c=99-x, since c=c:
x+9=99-x
2x+9=99
2x=90
x=45, and since c=x+9, c=54
So Charlie weighs 54 kg and his brother weighs 45 kg.
All I can find on this is that it would be 10/16 but thats not an awnser. hmmm