1.5x-y=110 (1) 9y-x=110 (2)
y=5x-110代入(2)
9(5x-110)-x=110
44x-990=110
44x=1100
x=25
2.3s-t=5 (1) 5s+2t=15 (2)
t=3s-5代入(2)
5s+6s-10=15
11s=25
s=25/11
3.3x=2y (1) 8x-3y=7 (2)
x=2y/3代入(2)
16y/3-3y=7
16y-9y=21
7y=21
y=3