In my opinion, i think the first one is the best one since we're cutting down on paper wasted in mails when its better to do it online.
"paying bills online instead of sending paper through mail"
A similar but separate notion is that of velocity, which the rate of change<span> of </span>position<span>. Example . If p(t) is the </span>position<span> of an </span>object<span> moving on a number line at time t (measured in minutes, say), then the average </span>rate of change<span> of p(t) is the average velocity of the </span>object<span>, measured in units per minute.</span>
