Let the capacity of tank B is x gallons.
Then capacity of tank A is 0.7x gallons.
Consider statement 2:
"Tank A if full has 14000 gallons". i.e capacity of tank A is 14000 gallons.
So 0.7x=14000 . This means that x= 20,000 gallons.
Therefore capacity of B is 20,000 gallons..
This statement would've been enough if they asked for capacities of tanks. But since they asked for amount of solution present in tank, we have to calculate further.
Consider statement 1:
"Tank A is 80% full and tank B is 40% full."
This means that tank A has 0.8*14,000 gallons and tank B has 0.4*20,000 gallons which are required.
Hence both the statements together are needed.