The prefix "milli" before any standard unit such as meters, grams, or seconds. Just means it takes 1000 "milli"units to make 1 standard unit. For example, 1 meter=1000millimeters.
Knowing this, let's cross multiply:
[tex] \frac{7000 millimeters}{1 month} * \frac{1 meter}{1000millimeters} = 7 meters [/tex]
(units that are the same and diagonal from each other cancel out)
So, the answer is: Last month, a coral reef grew 7 meters.
