You need to have the key pair inside the virtual box Linux machine and then you can run the command for ssh.
So, copy the key to the Linux machine and open the terminal where the key pair is present.
Then run the below commands for ssh:
sudo chmod 400 <key-pair name>
ssh -i ./<keypair.pem> <usernameof machine>:<IP address>
The above syntax will help you to ssh in to your instance from linux machinne.
For more information, check out this AWS Tutorial.