Eliminating a variable in an LP problem
Hi, I have the following problem that is solved, but I don't know how it gets to it. I'd really appreciate it if someone could show me.
Well, the LP problem says:
minimize f = 8x+10y+18z
0<=x<=9, 0<=y<=15, 0<=z<=3.
And then my teacher eliminates z, and he gets:
Well, I know how my teacher got to f=180+2x+y, but how did he get 42<=2x+3y<=60? I know 60 comes from 20*3 (to make 2/3 an integer), but I don't know where 42 comes from.