Question 253228
This is a mixture problem. Here is the table based on the information given. Remember that water is 0% acid.
solution . . . . .% . . . . . gram . . . . . %gram
acid . . . . . . .90 . . . . .12 . . . . . . .1080
water . . . . . . 0 . . . . . .X . . . . . . .0
mixture . . . . . 25 . . . . .12 + X . . . . .300 + 12X
We can now set 
1080 + 0 = 300 + 12X.
Solving for X< we get
780 = 12X
X = 65 grams of water.