MILLI = 1000th, so one millimeter is 1000th of a meter, namely, in 1 meter, there are 1000 mm.
so in 1.2 meters there are 1.2*1000 = 1200 mm.
to cut them into 3 equal sides is just a plain division, 1200 ÷ 3, gives us 400 mm.
and we can convert that back to meters by 400/1000 = 0.4 meters.
