A bullet-shaped object is formed from a cylinder with a curved top. The cylinder has radius a and is situated with its base on the (x, y)-plane, with the origin located at the centre of the base. The curved top of the bullet is given by the formula z = 3a − x^ 2/a − y ^2/a

and the density is given by D( (sqrt(x^2+y^2)/a) +1)

where a and D are constants.

Calculate the mass of the object.