Systems of equations with different slopes and different y-intercepts have one solution. plzzz explain a) always b) sometimes c) never

Y=2x+4, the slope is 2, A(0,4)-y intercept
y=x+2, the slope is 1, B (0,2)- y intercept

the system is 2x-y=-4
                      -x+y= 2
                     
                       x= -2
                        y=0   is the solution ( only one)