If I understand you correctly:
There are four brothers locked in a room. All are of different heights. Their average height is 76 inches. The first 3 brothers have a 2-inch difference between them, consecutively. The height difference between the third brother and the last brother (who is the tallest) is 6 inches.
first three brothers: x+(x+2)+(x+4)
tallest brother: (x+4)+6
all brothers: x+(x+2)+(x+4)+(x+4)+6=304
height of brothers in inches: 72, 74, 76, 82
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