The items don't matter but the proportions do. 16 fries (or filters) need 6 potatoes (or bottles), so 40 fries (or filters) need 40/16*6=5/2*6=5*3=15 potatoes (or bottles). In other words, 40 is two and a half times 16 (5/2) so I need two and half times potatoes or bottles.