How many days from 7-5-1980 to 7-5-2015.
First step is to find out how many years between the dates.
2015 - 1980 = 35
Multiply the number of years by 365 days in a year.
35 * 365 = 12775
Now we account for the extra day in each leap year.
35 / 4 = 8.75
There were 8 leap years (we don't count 1980 because
the start date is later than Feb 29).
12775 + 8 = 12783