If Wenzhou ships to Wencheng X, Wenzhou ships to Taishun 12-X, Hangzhou ships to Wencheng 8-X, and Hangzhou ships to Taishun X-2 (because the total number of units is18) x > =0， 12-X & gt； =0，8-X & gt； =0，X-2 & gt； =0,

30X+40(8-X)+50( 12-X)+80(X-2)& lt； =840，x < =4，

X & gt=0,12-x > =0，8-X & gt； =0，X-2 & gt； =0，X & gt=2

So the values of x are 2, 3 and 4.