Here it is — the formula this whole chapter runs on: $v = \dfrac{d}{t}$. Read aloud: v equals d over t. $v$ is the speed, $d$ the distance, $t$ the time — and a formula you can SAY is a formula you own, so say it now (quietly is fine, nobody's looking).

What it means is friendlier than it looks: speed is just distance shared out over the time it took. Walk 6 metres in 2 seconds and you were doing 3 metres each second — $6 \div 2 = 3\ \mathrm{m/s}$. You have done this math your whole life; now it has a uniform. Whenever a problem hands you a steady pace, a distance and a time, $v = \dfrac{d}{t}$ is the tool it is asking for.