Answer:
600
Step-by-step explanation:

x max = 
a = -5
b = 6
-6/2(-5) = 6/10 = 3/5 = .6
.6 thousand = 600
600 speakers should be sold.
Alternatively, you can check the vertex of the parabola formed.
The correct answer is 336 cubic inches.
6•8•5=240
9-5=4
4•6/2=12
12•8=96
240+96=336
From cm to km you divide the number by 100000
So 35,000/100000 = 0.35km
Area of the triangle base: (1/2)*3.3*x
area of the cone base: pi*3*3
they are equal, so 9pi=(1/2)*3.3x
x=17.1