Since Chiang Heng spent all of his money to buy seven items, the number of each item that he purchased is 19 items.
Since the total amount of money that Chiang Heng took to the store was $235 and he purchased a water bottle for $33, a keyboard for $34 and a dictionary for $35, the total amount of money that he has left after purchasing this three (3) items is given by;
Total amount of money left = Total amount of money - Total cost of three items
Total amount of money left = $235 - ($33 + $34 + $35)
Total amount of money left = $235 - $102
Total amount of money left = $133
Since Chiang Heng spent all of the money he has left to buy seven items, the number of each item that he purchased can be determined by dividing the total amount of money left by the number of items;
Number of items = Total amount of money left/7
Number of items = $133/7
Number of items = 19 items.