CUDA symlinks not working

Question

I'm trying to install CUDA on Ubuntu using this guide by @B0rk4:

How can I install CUDA 9 on Ubuntu 17.10

The relevant section is to create a symlink for gcc & g++:

sudo apt install gcc-6
sudo apt install g++-6
sudo ln -s /usr/bin/gcc-6 /usr/local/cuda/bin/gcc
sudo ln -s /usr/bin/g++-6 /usr/local/cuda/bin/g++

When I follow these steps I get an error:

ln: failed to create symbolic link '/usr/local/cuda/bin/g++': No such file or directory

How can I create these symlinks?

Thanks in advance - I would comment on the linked page, but I'd need 50 rep to do so.