title: Equivalent of observeOn and subscribeOn in Kotlin coroutines
body: <p>For example:</p>
  
  <pre><code>Observable.fromCallable&lt;Int&gt; {
     backgroundTask() // returns an integer
     }
     .observeOn(AndroidSchedulers.mainThread())
     .subscribeOn(Schedulers.io())
     .subscribe ({ number -&gt; /* success */ }, { error -&gt; /* fail */ })
  </code></pre>
  
  <p>Generally <em>doing a task on the background (another thread) and getting the result of it back in the main thread.</em></p>
  
  <p>How will this code snippet be using <strong>Kotlin coroutines</strong>?</p>