Error during CINEMAS installation

Hello.

So, I encountered an error during the installation of the program. It goes as follows:

I am currently working on Linux Mint 20 and when googling my situation it seems that libgfortran3 is no longer supported here, only its successor libgfortran5. I tried running the command shown on the terminal to install libgfortran3 anyways but it appears unable to locate package. Please advise on what I should do.

Thanks in advance.