mk_activity_grade_calculator.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <androidx.appcompat.widget.AppCompatEditText
        android:id="@+id/etMarks"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:hint="@string/hint_enter_your_marks"
        ...
    />

    <androidx.appcompat.widget.AppCompatTextView
        android:id="@+id/tvGrade"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        tools:text="Your Grade Is: A"
        ...
    />

    <androidx.appcompat.widget.AppCompatButton
        android:id="@+id/btSubmit"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:text="@string/submit"
        ...
    />

</androidx.constraintlayout.widget.ConstraintLayout>