A hollow ball floats in water in suspension. What is the mass of the ball if the volume of the cavity is Vp = 17.75?

It is known from the condition that a hollow copper ball floats in water. It is necessary to find what the mass of the ball is equal to if it is known that the volume of its cavity is equal to Vcavity = 17.75 cubic meters. units.
Let’s start by finding the volume of pure copper:
V (copper) = m / ρ₁, where ρ₁ = 8.92 g / cm³ – copper density, the value is constant.
Let’s apply the law of melting bodies, which can be written as:
mg = ρ₂g (V + (m / ρ₁)),
where V is the volume of the cavity inside the sphere, ρ₂ = 1 g / cm³ is the density of water, the value is constant.
Let us express the mass:
m = ρ₂V / (1 – ρ₂ / ρ₁) = 17.75 / 0.887 = 20 grams.