solve y=3x+4 and 7x+2y=21

Question

solve by substituting

y=3x+4

7x+2y=21

Answer 1

You gave the method to the solution in your question.

Solve by substituting
y=3x+4  INTO
7x+2y=21

 

7x+2y=21

becomes

7x+2(3x+4)=21

distribute

7x+6x+8=21

now solve for x