This is going at the simplest of the simple, and though I wouldn't suggest doing it, it's always an option.

Have 2 wheels angled at a 45 degree angle pointing upwards in the front of your robot, with a little room less than the diameter of the ball behind the wheels. You can now use the wheels to suck in balls, and shoot them up into the lowest basket.

Like I said, I wouldn't suggest doing it, but if you're out of ideas by week 3, then it may be something to look into.