This is a simple conversion from metres to kilo metres problem in which we should know how much metres is one kilo metre or how much kilo meters is one metres.
So in order to convert from metres to k m we just have to divide by 1000 as 1 km is equal to 1000 meters. Similarly for the other way round we have to multiply by 1000 as 1 metre is 0.001 km.
SO if Mary swims 850 metres each day then she swims around 0.85 km every day.
