6. (10 points) Arrange 8 numbers in a row from left to right. Starting from the third number, each number is exactly the sum of the two numbers before it. If the 5th number and the 8th number are 53 and 225, respectively, then the 1st number is $\qquad$ .
【Solution】Solution: According to the problem, we know:
Since the 5th number is 53, it indicates that the 7th number is 53 more than the 6th number, and the sum of the 7th and 6th numbers is 225.

Therefore, according to the sum and difference formula, the 6th number is: $(225-53) \div 2=86$.
So the 4th number is $86-53=33$.
The 3rd number is: $53-33=20$.
The 2nd number is: $33-20=13$.
The 1st number is: $20-13=7$.
Therefore, the answer is: 7