We look for a term in one of those equations that has a letter
with an understood coefficient of 1 or -1.

We see that  has a term x with a 1 understood 
coefficient.  

We solve for that letter by getting it alone on one side:

            

Subtract 2y from both sides
                

Now in the other equation , substitute (8-2y)
for x

           
           

Solve for y

           
           
               
               
               
                

Substitute (4) for y in the equation where you solved for x

                
                
                
                

So that means that the common solution to the pair of equations
is (x,y) = (0,4) 

It means that if you draw the graphs of the two lines they will
intersect at the point (0,4)





Edwin