React-Native Android demo app

I need an Android React-Native demo app. It should be as simple as possible with two methods: to transfer data from native (java) code to react-native (js) and vice versa. Both methods should return String. The job should be done in 3 hours from now. And I expect that you explain, how the things work, how react-native can communicate with native java code. You should be familiar with react-native and should have experience making react-native apps for android platform. I'm looking for a react-native expert, who can help me in the nearest future with real production apps. And you should have good communication skills in English or in Russian. Thanks! I'm looking forward to working with you!