You are correct: we are looking for 150q and 75w. But notice that

150q + 75w = 75(2q + w)

This is why we can safely say that we're actually interested in 2q + w, since the amount paid will be that number multiplied by 75.

1. means that you can find q: q will be 600/150 = 4. However, you still don't know anything about w, so 1 is insufficient.

2. tells you that q + w/2 = 12. I'd personally be tempted to eliminate that fraction over there and just multiply the whole equation by 2:
q + w/2 = 12
2q + w = 24 - and this is all we need to solve the whole problem, since the amount paid will be 24*75.