Question 415972
its substitution method...

substitute   y = 3x in the other equation


==>  y = x+ 4

==>   3x  = x + 4


3x -x  = x - x  + 4


2x  =  4


{{{2x/2  = 4/2}}}


==>   x = 2



==> y = 3(2)  = 6