如何在主线程上使用 Kotlin 协程 await()

I just started learning Kotlin coroutines and was trying to simulate some long time API-calls with showing the result on the UI:

class MainActivity : AppCompatActivity() {
    fun log(msg: String) = println("[${Thread.currentThread().name}] $msg")

    override
    fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        this.setContentView(R.layout.activity_main)
        val resultTV = findViewById(R.id.text) as TextView

        val a = async(CommonPool) {
            delay(1_000L)
            6
        }

        val b = async(CommonPool) {
            delay(1_000L)
            7
        }

        launch(< NEED UI thread here >) {
            val aVal = a.await()
            val bVal = b.await()
            resultTV.setText((aVal * bVal).toString())
        }
    }
}

I don't understand how could I possibly use launch method with main context.

Unfortunately, I was not able to find anything about delivering results for some specific threads on the official tutorial for coroutines.