Q. P and Q travels from D to A and break journey at M in between. Somewhere between D and M, P asks "how far have we travelled?" Q replies, "Half as far as the distance from here to M". Somewhere between M and A, exactly 300km from the point where P asks the first question, "How far have we to go?" Q replies, "Half as far as the distance from M to here". The distance between D and A is ?

1. 500 km
2. 250 km
3. 350 km
4. 450 km