6. (3 points) Xiao Hu placed chess pieces on the grid points of a $19 \times 19$ Go board, first forming a solid rectangular array. Then, by adding 45 more chess pieces, he formed a larger solid rectangular array with one side unchanged. How many chess pieces did Xiao Hu use at most?
A. 285
B. 171
C. 95
D. 57
【Analysis】 $45=1 \times 45=3 \times 15=5 \times 9$, since it is a rectangle, $1 \times 45$ does not need to be considered, so the length of the unchanged side of the rectangle could be: 3, 5, 9, 15, these four. To use the most chess pieces, the unchanged side length can only be 15, the longest side of the chessboard is 19 grids, so the final larger point array is $15 \times 19=285$ pieces.

【Solution】Solution: $45=1 \times 45=3 \times 15=5 \times 9$
Since it is a rectangle, $1 \times 45$ does not need to be considered, so the length of the unchanged side of the rectangle,
could be: 3, 5, 9, 15, these four,
To use the most chess pieces, the unchanged side length can only be 15, the longest side of the chessboard is 19 grids,
so the final larger point array is: $15 \times 19=285$ (pieces);
Therefore, the answer is: $A$.