Math Question

How do you solve the following systems of equations? 

x1 + x2 = 1
-x1 + x2 + x3 = 2
-1x2 + x3 = -1 

I tried using the below method but was unable to get it to solve properly. 

a) Interchange any two equations in the system.
b) Multiply both sides of any equation by a nonzero constant.
c) Multiply both sides of any equation by a nonzero constant and add the result to a
second equation in the system, with the sum replacing the latter equation.