July and August are 2 of the 12 months in the year. The growth for the year can be expected to be 6 times the growth in a 2-month period, so 60 cm.
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You could get down to particulars as to the number of days in those two months versus the total number of days in a year. You would have to specify whether it is a leap year. In a non-leap year, the growth might be ...
