Question 508576
 Solve each system.

1. 10x+6y=0
   -7x+2y=31
Multiply the 2nd eqn by 3, then subtract.

10x +6y=0
-21x+6y=93
------------- Subtract
31x = 93
etc.
------------
2. 7x+5y=18
   -7x-9y=4
-------------- Add them
===========================
------------
3. -3x+y=6
   6x-2y=25
Multiply the 1st eqn by 2
3.-6x+2y=12
   6x-2y=25
---------------- Add
0 = 37
That's not true, so the system is inconsistent.
--> no solution.  
If you graph them, you get parallel lines, no intersection, no solution.