First, we want to find the volume of the barrel. The formula for the volume of a cylinder is h* π * r^2. Substituting 15 in for h and 10 in for r, we get that the volume of the barrel is 1500π. Now, we must find the area fo the bucket. The formula for the volume of a hermisphere is (2/3)* π * r^3. Substituting 10 in for r, we get that the volume of the bucket is 2000/3π. We divide 1500π by 2000/3π to get 9/4, but Brad can't make 1/4 of a trip to the well and get water, so the answer is **3 trips**.