Question 82405
y=2x+3 now substitute (2x+3) for y in the other equation & solve for x.
-6x+3(2x+3)=12
-6x+6x+9=12
0x=12-9
0=3 now common solution here.
proof we plot the 2 lines
y=2x+3 (red line) &
3y=6x+12, y=6x/3+12/3, y=2x+4 (green line)
{{{ graph( 300, 200, -6, 5, -10, 10, y = 2x +3, y = 2x +4) }}} (graph 300x200 pixels, x from -6 to 5, y from -10 to 10, of TWO functions y = 2x +3 and y = 2x +4).