Monday count only

Question

I just want to count the dates Monday of each number in column C filtered by column A. But it is giving an error in the formula:

=NETWORKDAYS.INTL (JANEIRO!C2, "1"; FEVEREIRO!C2, "1 ")

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Answer 1

paste in A2 cell and drag down:

=ARRAYFORMULA(SUM(N(REGEXMATCH(""&TRIM(SPLIT(QUERY({JANEIRO!A$2:C; FEVEREIRO!A$2:C}; 
 "select Col1 where dayOfWeek(Col3) = 2"; 0); ",")); "^"&TO_TEXT(A2)&"$"))))

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