If you're asking the difference between 14 ft and 21 ft your answer is 7 ft, just subtract 14 from 21
The first few multiples of 8 are: 8, 16, 24, 32, 40, and 48. The first multiples of 12 are: 12, 24, 36, 48, 60, and 72.
Common multiple of 8 and 12 are 24 and every subsequent multiple of 24.
As 8×3=24
12×2=24
So 24 is a common multiple of 8 and 12 this means the other common multiples of 8 and 12 are the multiples of 24 like 48, 72, 96 etc.
The volume of any rectangular block is
(length) · (width) · (height) .
As long as the block of ice is rectangular,
its volume is
(3 meters) · (1.5 meters) · (2 meters)
= 9 cubic meters .
Note:
That little ice chip weighs roughly 9.9 tons !