How do I get the CUDA and cudNN version on Ubuntu 16.04 machine?

Question

I want to find out CUDA and cuDNN version on my linux machine. I have come across following commands :
cat /usr/local/cuda/version.txt
Above gives me verions 9.0.176

and

nvcc --version | grep "release" | awk '{print $6}'
Above gives me V7.5.17

Which is the right one ?