( 1)y =( 100-80-n)* a *( 1+0. 1 * n)
(2) According to (1):
y=a*(20-n)*( 1+0. 1n)
=a*(20+n-0. 1n^2)
When n=5, (20+n-0.1n 2) has the maximum value.
The maximum value is 22.5a, which should be satisfactory. .....