solve the following systems?

Question

x-y-2z= - 1
x+y+z= 6
x+y-z=4

Answer 1

add the 2nd and 3rd equations:
2x+2y = 10, which can be simpliefied to x+y =5,
now put it back in the seccond equation, but instead of writing x+y write just 5:
5+z =6 => z=1.
now we have reduced the problem to 2 equations:
x+y =5
x-y -2(1) =-1 (using the first equation)

x+y=5
x-y= 1
add them :
2x =6 => x=3
and now we can use x-y=1 with x=3 to find y:
3-y=1 => 3-1=y => y =2
so the solution is:
x=3, y=2 and z=1 .

Answer 2

x=3
y=2
z=1
!!!