Answer:
See below
Step-by-step explanation:
Sum of ingredients = sum of final solution
.50 x    where x =  50 percent amount   then 40 - x = 18% amount
.50 x   + .18(40 - x)  =  .30 ( 40 )
.50 x  + 7.2 - .18x  =  12
.32x  = 4.8
x = 15 L of 50% Â Â 25 liters of 18%