Answer:
0.5 pounds of butter.
Explanation
X pounds for 0.25 gallons.
0.5 gallon of cream - 1 pound of butter
0.25 gallons of cream - X pounds of butter
Applying cross multiplication:
0.5X = 0.25
X = 0.25 over 0.5 or 0.25/0.5
X = 0.5
Therefor, you could make 0.5 pounds of butter with 0.25 gallons of cream.