Exercise 12.1 Q3, $x - y - 4 = 0,\; 3x - 3y - 10 = 0$, has number of solutions —

Both equations reduce to $x-y=$ different constants ($x-y=4$ versus $x-y=\frac{10}{3}$), so the lines have equal slope but different intercepts. Being parallel and distinct, they never meet, so there is no solution.