Assuming there is no catch like some periods of 8 years get more Sundays that others (I'm not checking that out) then the following applies and would be a reasonable estimate.
8 years = 8 * 365.25 days = 2922 days approximately.
2922 / 14 = 208.7 fortnights, round it down to 208 alternate Sundays.
208 * $5 = $1,040.
Now you know the process you can memorise/understand it and work these things out for yourself.