20km -15dam .......m PAKAI CARAA PLEASE

20.000 m - 150 m = 19.850 m
1 km = 1.000 m
1 dam = 10 m

20 km = 20 × 1.000
=>>>>>> 20.000 m

15 dam = 15 × 10
=>>>>>> 150

pengurangan

20.000 m - 150 m
=>>> 19.850 m