40 common factors multiplication
keeping in mind that a year has 12 months, thus 6 months is really 6/12 of a year.

The answer should be A. 4 Meters
I hope this helps you
DF^2+DC^2=FC^2
DF^2+15^2=39^2
DF^2=39^2-15^2
DF^2=24.54
DF=36
55
-41
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14 that's the answer