For all real values of a and b, lines ((2a+b)x+(a+3b)y+(b−3a)=0 and mx+2y+6=0 are concurrent. Then m is equal to

Lines (2a + b) x + (a + 3b) y + (b - 3a)=0 or a(2x +y - 3)+ b(x + 3y + 1 ) = 0 are concurrent at the point of intersection of lines 2x+y-3 =0 and x+3y+ 1=0,which is (2,-1).Now, line mx + 2y + 6 = 0 must pass through this point.Therefore, 2m - 2 + 6 = 0 or m = -2.