Form 4-digit numbers $>6000$ using digits {0,5,6,7,8,9} without repetition. The first digit must be 6,7,8,9 (4 choices), remaining digits from rest (5P3 = 60).
Total = $4 \times 60 = 240$
Similarly, count 5-digit and 6-digit numbers formed from remaining digits (6P5 = 720, 6P6 = 720), add all: $240 + 720 + 480 = 1440$