Question

THIS

Answer 1

solve first 2 equation and solve it simultaneously and get the value of x
then solve the 2nd and 3rd equation simultaneously to get the value of z

Answer 2

Add equations 1 and 2 together. That will eliminate z.
Then multiply equation 2 by -1 and add it to equation 3. That will also eliminate z.
Now you have two equations in only x and y. Solve for x and y and then substitute values of x and y into any one of the original 3 equations and get z.