You measure the salt water in the tank to have a density of 1.02 g/mL. The balloon weighs 2.0 g and your weights have a mass of 30.0 g each. If you put 4 weights in your balloon, you must inflate the balloon to what diameter for it to have a density equal to the salt water, and therefore float in the middle of the tank?
Hint: Set the Volume of the Balloon equal to the equation for the volume of a sphere and solve for the diameter. V = 4/3(pi)(r)^3 and D= 2*r

Question

You measure the salt water in the tank to have a density of 1.02 g/mL. The balloon weighs 2.0 g and your weights have a mass of 30.0 g each. If you put 4 weights in your balloon, you must inflate the balloon to what diameter for it to have a density equal to the salt water, and therefore float in the middle of the tank? 
Hint: Set the Volume of the Balloon equal to the equation for the volume of a sphere and solve for the diameter. V = 4/3(pi)(r)^3 and D= 2*r