(3 × 8) × 6 = 3 × (8 × 6)
729-243=486
486×3=1458
1458+729=2187(x=7)
1458×3=4374
4374+2187=6561(x=8)
4374×3=13122(average rate of change for interval 8 to 9)
13122+6561=19683(x=9)
Ans: B