We halve the diameter of 6 to get a radius of 3, and are given a height of 10. As we have two hemispheres, we can combine them into one sphere, so we would take the volume of a sphere with r=3 and add it to the volume of a cylinder with r=3 and h=10. Volume of a sphere is (4/3)pi*r^3 and volume of a cylinder is pi*r^2*h. Plugging in our values and adding, we get . This makes your answer 126*pi inches, which is roughly 395.841 inches.
The central angle of this is 112 degrees. That is CAE is 112 degrees. That being the case, CDE is 90 + 90 + 112 = 292 Tangents make a 90 degree angle with the center of the circle.