[tex]\bf \cfrac{12\underline{m}}{\underline{s}}\cdot \cfrac{km}{1000\underline{m}}\cdot \cfrac{60\underline{s}}{min}\implies \cfrac{12\cdot km\cdot 60}{1000\cdot min}\implies \cfrac{720km}{1000min}\implies 0.72\frac{km}{min}[/tex]
notice, the units that cancel
the units of conversion, is hmm say there are 60secs to a minute, so 60s/m or you can also use it as m/60s,
depending on what unit you need cancelled, in this case, we needed the seconds cancelled, so we put the seconds atop, so it cancels with the one at the bottom, and so on.
there are 1000meters in 1km, so 1000m/km or km/1000m,
depending on what unit you need cancelled.
