35+28+29=92 yuan.
Ding Ding sent 35 yuan and added Dongdong, which not only filled in 35 yuan but also added 28 yuan, indicating that Dongdong has: 35+28=63 yuan.
Dongdong is worse than 29 yuan, so the price of this set of books is much higher than Dongdong's. 29 yuan: 63+29=92 yuan.
It is recommended to draw pictures for understanding.