⇒31(221+331)÷92(381−1121)⇒31(25+310)÷92(825−1213)⇒31(2×35×3+3×210×2)÷92(8×325×3−12×213×2)⇒31(615+620)÷92(2475−2426)⇒31(615+20)÷92(2475−26)⇒31(635)÷92(2449)⇒6×335×1÷24×949×2⇒1835÷21698⇒1835×98216⇒9835×18216⇒145×12⇒1460⇒730⇒472
Hence, 31(221+331)÷92(381−1121)=472.