15. Xiao Wang got full marks in the final exam, but when the teacher was marking the paper, Xiao Wang suddenly found that when he was doing a math fill-in-the-blank problem, the final result was a number multiplied by 8 and then subtracted from 63. Because of carelessness, he treated multiplication as division and subtraction as addition, but the number was right. The number of this math problem is _ _ _ _ _ _ _ _ _ _.

17. Divide a group of people into three groups: A, B and C. Everyone must be in one group. It is known that the average ages of A, B and C are 37, 23, 465 and 438+0 respectively. The combined average age of group A and group B was 29 years old. The total average age of group B and group C was 33 years old. Then the average age of this group of people is _ _ _ _ _ _.

18. The sixth-grade students of Le Ballon Rouge Primary School in Tianjin participated in the sports meeting, and everyone chose two of the three events: long-distance running, sprint and relay. It is known that there are 28 people who take part in long-distance running, 25 people who take part in sprint and 33 people who take part in relay. Then, there are _ _ _ _ _ who take part in long-distance running and relay events.

20. Xiao Zhang and Xiao Liu design a set of computer software together, and the reward of * * * is 1 120 yuan. Xiao Zhang works 10 days, Xiao Liu works 13 days, and Xiao Zhang's four-day salary is equal to Xiao Liu's six-day salary. How much does everyone get?