Answer:
10 liters
Explanation:
#The amount of pure juice is obtained by multiplying its proportion by the total:

#To make a blend of 80% means that the proportion of juice in the new blend is 80%.
-Juice is 4x the amount of water added.
Water=10-6=4 liters.
=>Amount of pure juice in the blend=4*4=16 liters
#Additional juice=Proportion- 6
=16-6
=10 liters
Hence, 10 liters of juice have to be added to achieve a 80% blend.