What's 1 m - 9 cm in the metric system

And also what is 2 km - 100 m in the metric system?
8 cm - 12 mm in the metric system?

1 m = 100 cm, so 1 m - 9 cm = 100 cm - 9 cm. Answer: 91 cm

2 km - 100 m = 2000 m - 100 m. Answer: 1900 m

8 cm - 12 mm = 80 mm - 12 mm. Answer: 68 mm