Category: Math and trigonometry
Adds its arguments
SUM(number1,[number2],...)
Category: Text
Formats a number and converts it to text
TEXT(Value you want to format, “Format you want to apply to that value”)
Category: Lookup and reference
Returns the row number of a reference
ROW([reference])
Category: Lookup and reference
Returns a reference indicated by a text value
INDIRECT(ref_text, [a1])
0
The formula checks for each date if it is Sunday using TEXT() function and then return and array of zero and ones that is summed up to give you the answer