Destiny has 4 liters of 49% acid. How much water should she add to make a solution that is 14% acid?

Destiny has 4*.49 = 1.96 L of acid. In order for the 1.96 L of acid to be 14% of the solution, there must be 1.96/.14 = 14 L of solution.

Destiny must add 14 L - 4 L = 10 L of water to make the desired solution.

The key here is that the amount of acid doesn't change.

add x liters of water, you have the total amount of liquid (x+4) liters

4*49% = (4+x) * 14%

0.14x=1.96-0.56

x=10

she needs to add 10 liters of water