Question 637537
I am to assume that the problem meant to say that you have to mix 4 parts of powder to 96 parts of water, measuring by volume.
That is a 1:24 ratio ({{{4/96=1/24}}}).
For the 2 scoops (1/2 cup) of powder Daniel added, he should have used 12 cups ({{{24*(1/2)=12}}})
There are 4 cups in a quart, so Daniel should have used 3 quarts of water ({{{12/4=3}}}).
Since Daniel only added 2 quarts, he needs to add 1 quart more.
There are 4 quarts in a gallon, so Daniel needs to add {{{highlight(1/4)}}} gallon of water.
 
NOTES:
To a chemist, like me, the problem sounds wrong. With any scientifically sound interpretation of the wording, it would impossible to solve  due to lack of information.
96% water would mean 96 grams of water mixed with 4 grams of powder, making 100 g mixture, and if w/w (weight in weight) were specified, it would be even clearer.
The density of water can be assumed to be 1.00g/mL, but we do not know the bulk density of the powder, so we do not know how many grams of powder were used.
 
It would be worse if the drink had to be 4% powder w/v (weight in volume, meaning 4 g powder in 100 mL final drink volume), beause we would not know the density of the correctly formulated drink.