If a bicycle travels 800m in a time of 72 seconds how fast is it moving

It's traveling at a rate of  800 meters per 72 seconds.

For a more familiar unit, do the division:

                         (800 meters) / (72 seconds)

                     =  (800 / 72)  meters/second

                     =    (11 and 1/9) m/s

                       (about  25.9 mph)

This is what a calorimeter is used for simpler ex, to measure calories in food.

The independent variable would be the fertilizer as it is what the dependent variable (the growth of grass) depends on.