50 points and brainiest if correct.

Answer:
28 gallons.
Step-by-step explanation:
1/5 is 20% of the container's full capatcity.
7/10 is 70% of the container's full capatcity.
20% - 70% = 50%
By adding 14 gallons of water, the container's water went up by 50%.
If we multiply 14 by 2, we will know what the container can hold at 100% capatcity.
14 x 2 = 28