以下を試しましたが、最後にエラーが発生します。4.8.2 が干渉していないことを確認するために、それを削除しました。
どんな提案も素晴らしいでしょう！
sudo add-apt-repository ppa:ubuntu-toolchain-r/test
sudo apt-get update
sudo apt-get install g++-4.9
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
g++-4.9 : Depends: gcc-4.9-base (= 4.9.2-0ubuntu1~14.04) but 4.9.2-10 is to be installed
Depends: gcc-4.9 (= 4.9.2-0ubuntu1~14.04) but it is not going to be installed
Depends: libstdc++-4.9-dev (= 4.9.2-0ubuntu1~14.04) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.
idf@C55t-A:/etc/apt$