200-(x- 10)20(x-8)=700

(400-20 times) (x-8)=700

(20-x)(x-8)=35

20x- 160-x？ +8x=35

x？ -28x+ 195=0

x= 13，x= 15

(2)200-(x- 10)20(x-8)=-20x？ +560x-3200=-20(x- 14)？ +720

X= 14 is the maximum.