6. As shown in the figure, in a 5 $\times$ 5 square, there are 21 empty cells. It is known that positive integers can be filled in the empty cells so that each row and each column forms an arithmetic sequence. What number must be filled in the cell marked with a star?

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6. As shown in the figure, in a 5 $\times$ 5 square, there are 21 empty cells.  
It is known that positive integers can be filled in the empty cells so that each row and each column forms an arithmetic sequence.  
What number must be filled in the cell marked with a star?
$6 .(142)$
Let $a$ and $b \%$ be the numbers that fill in the blanks. From $b-2a$, and the common difference of the first row being $2b-a-74$, we get
$$
2a+4(b-2a)=186
$$

and $a+2(2b-a-74)=103$.
Solving these equations, we can find the numbers that fill in the blanks in the figure. Therefore, the number that should be entered at the starred position is 142.