Question

How long does it take to travel 100km at a speed of 80 km/h?

Answer 1

Speed = distance/time,
You can kind of tell that, because the units of speed is km/h ( or m/s, or miles/hour — depending on the situation).

Now if you apply your algebra skills, you might discover that

time = distance/speed

Plug in the data:
time = 100 km / (80 km/h)
After application of algebra skills again you can see that the units will simplify to simply h.
time = 1.25 h