What is the greatest possible length which can be used to measure exactly the lengths 18 m, 40 m and 6 m 50cm?	Choose the correct choice from the following:
A) 20 cm  B) 23 cm  C) 25cm  D) 10 cm  E) 28 cm
Required length = HCF of 1800 cm, 4000 cm, 650 cm = 50 cm   Answer is 10 cm
<result>D</result>
What is the greatest possible length which can be used to measure exactly the lengths 18 m, 40 m and 6 m 50cm?