Delta x over Delta t

v_{\text{avg}} = \frac{\text{distance traveled}}{\text{time elapsed}}

v_{\text{avg}} = \frac{\Delta x}{\Delta t}

v_{\text{avg}} = \frac{x_{\text{final}} - x_{\text{initial}}}{t_{\text{final}} - t_{\text{initial}}}

v_{\text{avg}} = \frac{80-30}{3-2}

v_{\text{avg}} = 50 \text{mph}