- from (ii)
- $3 x+y=30$
- put $y=0 \Rightarrow x=30$
- $ x=0 \Rightarrow y=90$
- $\therefore$ points on line $3 x+y=90$ are (30,0) & (0,90)
- Corner points are
- O(0,0), A(30,0), B(20,20) \& C(0,50)
- $ Z_0=0$
- $ Z_A=4 \times 30+0=120 \text { (largest value) }$