To give us a basis of comparison in arranging the given values from smallest to largest, we should expressed all values in one unit only. For this case, let us convert all units in terms of mm so that we can compare.
We know that:
1 m = 10 dm = 100 cm = 1000 mm
Therefore,
A. 7 cm --> 7 cm (1000 mm / 100 cm) = 70 mm
B. 18 mm
C. 1 m --> 1 m (1000 mm / 1 m) = 1000 mm
D. 3 dm --> 3 dm (1000 mm / 10 dm) = 300 mm
Since they are now expressed in same units, we can arrange the numbers from smallest to largest:
18 mm, 7 cm, 3 dm, 1 m