1)
I:3x-y=4
II:2x+y=11
add both equations together:
3x-y+2x+y=4+11
3x+2x=15
5x=15
x=3
insert x=3 into I:
3*3-y=4
9-y=4
5=y
(3,5)
2)
I:4x-14y=6
II:-2x+7y=-3
multiply II*(-2):
4x-14y=6
-> II*(-2)=I
-> infinite solutions=last option
3)
I: 7l+4s=150
II: s+l=30
it's the first option
