SUMIF(A1: A4; "=0"; B1: B4) sums all values in range B1: B4 if the corresponding value in A1: A4 matches =0
SUMIF( A1: A4; "=0"; B1: B4) telt alle wearden yn B1: B4 by inoar op as de byhearrende wearde yn A1: A4 gelyk is oan 0