There is a box of ping-pong balls, one of which is heavy and defective. Weigh it with a balance. It is guaranteed that the heavy ping-pong ball can be found after 3 weighings. How many ping-pong balls are there in this box?
有盒乒乓球，其中有一个较重的是次品，用天平称，保证称3次就能找到这个较重的乒乓球，这盒乒乓球可能有多少个？
<result>10</result>