Too many zeros converting from ml to l
1 scoop of powder with 330ml of milk equals tasty drink.
300 scoops in 10 pounds is 100l
Whether or not you need protein shakes depends on your fitness goals. If your trying to gain mass and/or get stronger, then I definitely think protein shakes help. As someone stated earlier, a general rule of thumb when trying to gain mass is to intake daily a gram of protein for each pound you weigh. It can be difficult to eat that much protein from solid food in a single day, especially when you consider the time it will take to prepare and cook everything, or having to lug around all those prepared meals to the office or around campus if you're still in school. A protein shake can be more convenient at times.
If you're less concerned about gaining mass, and simply want to lose weight and tone your physique, then it's probably not necessary to intake additional protein outside of your normal meals (assuming you're already incorporating good protein sources like chicken breast in those meals).
And as a side note, regardless if you're trying to bulk or if you're trying to lean down, eating more often (i.e. 5-6 meals daily) is always recommended, as it helps boosts your metabolism, and you are less likely to binge eat than if you were to eat 2 or 3 meals a day.