Answer :
1. 7x+15y=32
2. x-3y=20/*5
2. 5x-15y=100
1.+2.= >12x=132
x=11
1. 7*11+15y=32
15y= -45
y= -3
x=11;y=-3
2. x-3y=20/*5
2. 5x-15y=100
1.+2.= >12x=132
x=11
1. 7*11+15y=32
15y= -45
y= -3
x=11;y=-3
{7x+15y=32
{x-3y=20 /*5
{7x+15y=32
{ 5x-15y=100 (+)
7x+5x+15y-15y=32+100
12x=132 /:12
x=11
x-3y=20
11-3y=20 /-11
-3y= 9 /:(-3)
y=-3
The solution: (11; -3)