a) 90 m + 60 m = 150m
40 dam + 5 dam = 45 dam
900 cm + 630 cm = 1530 cm
750 m + 130000 m = 130750 m
43 dam + 6 dam = 49 dam
b) 720 m - 140 m = 560 m
187 hm - 21 hm = 166 hm
57000 cm - 16000 cm = 41000 cm
900 dam - 90 dam = 810 dam
6300 mm - 120 mm = 5100 mm
210000 dm - 1800 dm = 208200 dm