Volume of the balloon is
V = 4?r3/3
  = (4)(?)(5.1 m)3 / 3
  = 555.36552 m3
The density of helium,?helium = 0.179
kg/m3
The density of airm, ?air = 1.29 kg/m3
The mass of the balloon, m = 2.8 kg
The air's weight equal to mg
  Wair = ?air V g
          =
(1.29 kg/m3)(555.36552 m3)(9.8
m/s2)
          =
7020.93 N
The weight of balloon including helium is
  Whelium = mg+?helium V
g        Â
            Â
= (2.8 kg)(9.8 m/s2) + (0.179
kg/m3)(555.36552 m3)(9.8
m/s2)
                =
1001.66 N
Therefore maximum weight it can lift is
maximum weight lift = Wair
-Whelium
          Â
= 7020.93 N - 1001.66 N
         = 6019.27
N
