how much water should be added to 13 liters of a 20 % - solution of alcohol to reduce the concentration of alcohol in the solution by 75 % ?
n0 = 13.0
n1 = 20.0
n2 = 75.0
t0 = n2 / 100.0
t1 = 100.0 * 2.0
t2 = n1 * t0
t3 = n1 - t2
t4 = t1 / t3
answer = t4 - n0
print(answer)