well, the balloon original was of radius = 2 = r, he then put it 1 cm extra twice, so it went up to 4 = r. The balloon original had a radius of 2 and then it went up to 4.
[tex]\bf \textit{volume of a sphere, \underline{originally}}\\\\ V=\cfrac{4\pi r^3}{3}~~ \begin{cases} r=radius\\[-0.5em] \hrulefill\\ r = 2 \end{cases}\implies V=\cfrac{4\pi (2)^3}{3}\implies V=\cfrac{32\pi }{3} \\\\\\ \textit{volume of a sphere, \underline{later on}}\\\\ V=\cfrac{4\pi r^3}{3}~~ \begin{cases} r=radius\\[-0.5em] \hrulefill\\ r = 4 \end{cases}\implies V=\cfrac{4\pi (4)^3}{3}\implies V=\cfrac{256\pi }{3} \\\\[-0.35em] ~\dotfill[/tex]
[tex]\bf \cfrac{\textit{later on}}{\textit{originally}}\qquad \qquad \cfrac{\frac{256\pi }{3}}{~~ \frac{32\pi }{3}~~}\implies \cfrac{256\pi }{3}\cdot \cfrac{3}{32\pi }\implies 8[/tex]
