Question 835084
m+b=9,
m=9-b

m*b^2=y
(9-b)*b^2=y
9 b^2-b^3 = y
derivative 
18b-3b^2=0
18b=3b^2
18=3b
6=b

max{(9-b) b^2 = y} = 108 at b = 6