Please help System of Equation in Three variables?

1) 2a+c=-10 b-c=15 a-2b+c=-5 2) x+y+z=3 13x+2x=2 -x-5z=-5 3)x-y+3z=3 -2x+2y-6z=6 y-5z=-3 4)3x-2y+z=1 -x+y-z=2 5x+2y+10z=-39 5)3x-2y+z=1 -x-y-z=-3 3x-2y+3z=-12