The best thing ever is Photomath! Go to the app store on your phone, tablet, etc. and download Photomath. It literally does all your math for you and even shows the steps!! I use it all the time. :)
Let's plug in y=3x-7 into 2x+4y=14 2x+4 (3x-7)=14 Distribute 2x+12x-28=14 Add 14x-28=14 Add 28 to both sides 14x=42 Divide X=3 Y=3 (3)-7 Y=9-7 Y=2 (3,2) A the solution is (3,2)