countif

COUNTIF counts cells that meet one condition — it's built specifically to answer "how many rows match this criterion," as distinct from SUMIF/SUMIFS (which total a different column based on a condition) or plain COUNT (which only counts numeric cells, regardless of their value). Marks: correct function (1), correct range in column C (1), correct criterion "Platform" (1). Put the criterion in quotes, because Excel treats an unquoted word as a reference to a named cell or range rather than literal text to compare against — quoting it tells Excel explicitly "this is a text value, not a name." COUNT would be wrong because it counts numbers only, and "Platform" is text, so COUNT would return zero regardless of how many rows actually say Platform.