Steam doesn't launch because it needs additional packages

I installed Steam using Ubuntu Software Center, but when I tried to launch it, it says it needs additional packages.

The error in the terminal:

Steam needs to install these additional packages: 
    libgl1-mesa-dri-lts-quantal:i386, libgl1-mesa-glx-lts-quantal:i386
sudo: unable to change to sudoers gid: Operation not permitted
sudo: setresuid() [0, 0, 0] -> [115, -1, -1]: Operation not permitted

sudo: unable to change to sudoers gid: Operation not permitted
sudo: setresuid() [0, 0, 0] -> [115, -1, -1]: Operation not permitted
Press return to continue:

What am I supposed to do?

I don't know anything about getting Steam working, but since it's saying it needs packages that you don't have installed, try installing them:

sudo apt-get install libgl1-mesa-dri-lts-quantal libgl1-mesa-glx-lts-quantal

If you're not comfortable running that command in a terminal, open the software center, look for these two packages, and install them:

libgl1-mesa-dri-lts-quantal
libgl1-mesa-glx-lts-quantal