An error occurred while trying to create a variable with audio (Android, Konlin)

Question

I try to assign the value to the variable into viewpage2 adapter. But there is an error into the line: val mediaPlayer = MediaPlayer.create(this, leter.sound) Here is chunk of my code:

class DetailViewPagerAdapter(
private val lettersList: List<Letters>,
private val activity: DetailActivity,
viewPager2: ViewPager2
) : RecyclerView.Adapter<DetailViewPagerAdapter.DetailViewHolder>() {

class DetailViewHolder(
    itemView: View
) : RecyclerView.ViewHolder(itemView) {

    val toolbar: Toolbar = itemView.findViewById(R.id.detail_toolbar)
    private val banner: ImageView = itemView.findViewById(R.id.detail_image_view)
    private val title: TextView = itemView.findViewById(R.id.title_detail_text_view)
    private val sample_detail: TextView = itemView.findViewById(R.id.sample_detail)
    private val description: TextView = itemView.findViewById(R.id.letter_description)
    private val playButton: ImageButton = itemView.findViewById(R.id.playButton)

    fun bind(
        leter: Letters
    ) {
        val mediaPlayer = MediaPlayer.create(this, leter.sound)
        banner.setImageResource(leter.banner)
        title.text = leter.title
        sample_detail.text = leter.sample
        description.text = leter.description
        toolbar.title = leter.title
        playButton.setOnClickListener {
            mediaPlayer.start()
        }
    }
}

Android studio marked the create underline red. And I can not understand how to solve the issue. Please help to understand why this does not work properly.