10. The teacher took out 13 cards, with the numbers on the cards ranging from 1 to 13. After keeping one of the cards, the teacher distributed the remaining 12 cards to three students, Jia, Yi, and Bing, with each receiving 4 cards. It is known that the sum of the numbers on the cards in Jia's hand and the sum of the numbers on the cards in Yi's hand are in the ratio of $2: 7$, and the sum of the numbers on the cards in Bing's hand is 4 times that of Jia's. Therefore, the number on the card kept by the teacher is $\qquad$
$6$