I2{=INDEX(C:C,MATCH(1=1,SUMIF(OFFSET(A$2,,,ROW($1:$9)),G2,B$2:B$9)>=20000,)+1)
另解{=INDEX(C:C,MATCH(1=1,SUMIF(OFFSET(A$2,,,ROW($1:$9)),G2,B$2)>=20000,)+1)