A bookshop was selling some calendars. The bookshop could make a profit of $18 from the sale of each calendar. After selling some calendars, the selling price of the remaining calendars was reduced by $10 each. The number of remaining calendars was 2/3 of the number of calendars sold at the original price. The bookshop made a total profit of $2870 after selling all the calendars. How many calendars were sold altogether?
original price : lowered price
3 : 2
18 * 3 = 54
18 - 10 = 8
8 * 2 = 16
54 + 16 = 70
2870/70 = 41
3 + 2 = 5
5 * 41 = 205