That amount of cannonballs would certainly get you a large amount of xp but surely not enough for 75. It is also an expensive method so id suggest ranging trolls/fire giants with iron knives/arrows+ would be a hell lot cheaper and would not take aslong as you think. Good luck.
There are many ways for you to get to 75. Some Expensive and some cheap.
Use a bow/iron knives at Fire Giants, you don't need to finish Waterfall Quest if your a pure ranger. This is cheap, and you may get dragon drops.
This method is expensive, i've been told if you have a dark bow, you can range Dark Beasts without 90 Slayer. If its true, you should buy a dark bow and range them. You may get 2 Dark Bow drops, as now you have 3. You can make a profit back, if this is possible.
im not so sure, at lv 40-50 is like 1.5k c balls with ranging, so thats almost the same xp per lv! so i think 1k cb will raise u 1 lv some, i dont think it will get u past 67 sorry