Carl lives 2 blocks from Ben, and Ben lives 8 blocks from Al. Since Al's house is at position 0, Ben's possible locations are 8 blocks to the east (positive direction) at position 8, and Carl's possible locations are 2 blocks to the west (negative direction) from Ben's location at position 6.
Therefore, the possible locations for Carl's house are at positions -6 or 6 on the number line.