Paypal openssl keys

I’m working with the paypal gem and have created the openssl keys for
testing through the sandbox. I’ve included the following lines per the
instructions in my controller:

@business_key = File::read(“business_key.pem”)
@business_cert = File::read(“business_cert.pem”)
@business_certid = “Z9EFBYAK59D234”

It’s returning this error:
No such file or directory - business_key.pem

Where should the key files reside in my rails app? Sorry for such a
simple question, but everything I’ve tried fails.