A sum become 49 times at certain rate of compound interest in 72 year in what time it will become 16807 time at same rate of compound interest ?

If a sum becomes 49 times in 72 years at compound interest, and 49 = 7², it means the amount doubles every 36 years (since 72 years gives 7²). We need 16807 = 7⁵. From 7² to 7⁵, we need 3 more doubling periods: 3 × 36 = 108 years. Alternatively: In 72 years, amount multiplies by 7². For 16807 = 7⁵, we need 5 doubling periods of 7. Since 72 years gives 2 periods, each period takes 36 years. For 5 periods: 5 × 36 = 180 years.