Answer: 7830 balls
Outer radius R = 30 cm, inner radius r = 30 − 2 = 28 cm, length h = 90 cm.
\[V_{\text{tube}}=\pi(R^2-r^2)h=\pi(900-784)\times90\]
\[=10440\pi\ \text{cm}^3\]
Volume of one ball \(=\tfrac43\pi(1)^3=\tfrac43\pi\).
\[\text{Number}=\frac{10440\pi}{\frac43\pi}=10440\times\frac34=7830\]