-3ab²(-a²b-3a²-ab²)-3ab²(-a²b-3a²-ab²)=3a³b³+9a³b²+3a²b⁴+3a³b³+9a³b²+3a²b⁴=6a³b³+18a³b²+3a²b⁴+3a²b⁴=6a³b³+18a³b²+6a²b⁴
-3ab²(-a²b-3a²-ab²)-3ab²(-a²b-3a²-ab²)=3a³b³+9a³b²+3a²b⁴+3a³b³+9a³b²+3a²b⁴=6a³b³+18a³b²+3a²b⁴+3a²b⁴=6a³b³+18a³b²+6a²b⁴