A shop charges a fixed delivery fee of 9 taka plus 3 taka for each notebook. If the total cost is 21 taka, how many notebooks were ordered?
Note
Let x be the number of items. The equation is 9 + 3x = 21. Subtract 9: 3x = 12. Divide by 3, so x = 4. The fixed fee is not part of the item count.