Alright, so the hard part here is probably setting up the proportion. Well, the first proportion is 6 cups of water to 4 cups of flour, which will look like this:
[tex] \frac{6 cups H2O}{4 cups flour} [/tex].
Now you'll have to set up the second proportion, since you're gonna use 6 cups of flour. So the second proportion will look like this: [tex] \frac{x cups H2O}{6 cups flour} [/tex]. x is the number you'll be solving for.
Set the two proportions equal to each other and solve for x. Good luck!