Two speeds rule the road: physics thinks in $\mathrm{m/s}$, road signs shout in $\mathrm{km/h}$. The bridge between them is exact: an hour is 3600 s and a kilometre is 1000 m, and 3600/1000 = 3.6. So $1\ \mathrm{m/s} = 3.6\ \mathrm{km/h}$ — m/s to km/h multiplies by 3.6, km/h to m/s divides.

The rule that saves marks: convert BEFORE the sockets. A formula's units only cancel when every input agrees, and a km/h number dropped into an m-and-s machine is the single most common exam wound. From here on, some questions hand you the wrong flavour on purpose.