Solve the quadratic equation: 3x2 + 60x − 14400 = 0.

$$\frac{3x^2}{3} + \frac{60x}{3} - \frac{14400}{3} = \frac{0}{3}$$ $$x^2 + 20x - 4800 = 0$$

We need two numbers that multiply to $-4800$ and add up to 20. These numbers are 80 and $-60$.

$$(x+80)(x-60) = 0$$

$$x+80 = 0 \implies x = -80$$ $$x-60 = 0 \implies x = 60$$

The solutions for $x$ are $\boxed{x = -80 \text{ or } x = 60}$.