Would be easier to interpolate that into the string:

```ruby
args << "--with-ssl-dir=#{Formula.factory('openssl').opt_prefix}" if build.include? 'with-homebrew-openssl'
```

Using the opt_prefix is probably also preferable - it's a link to the latest version of the OpenSSL keg, whereas `#prefix` would point to the specific version that's installed at the time of the openssh install.