29. There are 4 cards, each with a different number written on it. The doctor first distributes these 4 cards to four children: Damao, Ermao, Sanmao, and Simaoyi, then collects them back and redistributes them. This process is repeated 3 times. If the sum of the numbers on the cards received by Damao over the three rounds is 0, by Ermao is 3, by Sanmao is 11, and by Simaoyi is 16, what is the largest number on the cards? $\qquad$
answer: 7