Express your answer in smaller unit 800 m 35 cm - 154 m 49 cm

800 m  times the meter to cm conversion factor would be:

                                         100 cm
                         (800 m) *  = 80000 cm
                                             1 m

So 800 m 35 cm would be 80035 cm.

Likewise, 154 m would be 15400 cm, and so 154 m 49 cm would be 

 15449 cm.

Subtracting 15449 cm from 80035 cm, we get 64586 cm.

This is one way in which to do this problem.

We could convert 64586 cm back to meters:  645 m 86 cm

Dwould be the answer