Typcasting should work here and is the right thing to do, change:

$B->add( $A );

to

$B->add( (string) $A );

If php was a typed language and you could define add() like this:

public function add(string $content)

then you would not need to explicitly cast objects as above.

relying on the php team of developers to get things right first time always leads to issues so make your code as exact as possible.

Had I read this sooner, I would’ve known I didn’t need to alter the actual echoes. Just the other strings.

Try booting the VM in another PC, then something like:
apt-get update
apt-get install linux-generic

this will install the ‘generic’ version of the kernel (that you can select as default) to boot on your laptop.

Hope that helps.