Atortoise is walking in the desert. it walks
6.4 meters in
4 minutes. what is its speed?

It's speed is exactly 6.4 meters per 4 minutes.

In the more familiar units, that's

       (6.4 m / 4 min) = 1.6 meters per minute

(1.6 m / min) (100 cm/m) ( 1 min / 60 sec)  =  2-2/3 cm per sec.

                                                                       (1.05 inch per second, rounded)

                                                                       (160.3 furlongs per fortnight, rounded)