Hello Maryren,
Based on your profile, you are using Excel 2007, so take a look on AVERAGEIFS.
=AVERAGEIFS(AverageColumn,Location,"A",Number,123)
If you need compatibility with pre 2007 versions, could use this Array Formula with CTRL+SHIFT+ENTER
=AVERAGE(IF(Location="A",IF(Number=123,AverageColumn)))
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