Question 7
Let the 20% be represent by x. (l) is liters.

0.12(160)= 0.2X  (this 20% as a decimal)

=19.2 = 0.2x  (Divide both sides by 0.2 to have x alone.)
             
=19.2/.2

 x = 96

 Subtract the 96(l) from 160(l) = 64(l)of water.

 Evaporate 64(l) and leave 96(l).