Place a number in each of the following empty boxes so that the sum of the numbers in any 3 consecutive boxes is 53.9. What is the number that should go in the box with the question mark?

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DUI LIII SUO
Câu số 7
Place a number in each of the following empty boxes so that the sum of the
numbers in any 3 consecutive boxes is 53.9. What is the number that should
go in the box with the question mark?
Answer:
12.3
25.1 ?
..(Write your answer as a decimal in the simplest form)