V=\frac{4}{3}\pi r^3
r_1=3cm
V_1=\frac{4}{3}\pi *3^3=\frac{4}{3}\pi *9=4\pi *3=12\pi[cm^3]
r_2=6cm
V_2=\frac{4}{3}\pi *6^2=\frac{4}{3}\pi * 36=4\pi * 12 = 48\pi[cm^3]
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V_3=V_1+V_2=12\pi + 48\pi = 60 \p [cm^3]
\frac{4}{3}\pi r^3=60\pi |*3
4\pi r^3=180\pi |:4 pi
r^3=45
r=\sqrt[3]{45}[cm] <–odpowiedź
r \approx 3,56[cm]