Compilation failed

[chuwe1]

e: E:\WorkSpace\Berui\Kotlin Koans\Builders\Html builders\src\Task.kt: (2, 12): Unresolved reference: html
e: E:\WorkSpace\Berui\Kotlin Koans\Builders\Html builders\src\Task.kt: (3, 9): Unresolved reference: table
e: E:\WorkSpace\Berui\Kotlin Koans\Builders\Html builders\src\Task.kt: (4, 13): Unresolved reference: tr
e: E:\WorkSpace\Berui\Kotlin Koans\Builders\Html builders\src\Task.kt: (5, 17): Unresolved reference: td
e: E:\WorkSpace\Berui\Kotlin Koans\Builders\Html builders\src\Task.kt: (6, 21): Unresolved reference: text
e: E:\WorkSpace\Berui\Kotlin Koans\Builders\Html builders\src\Task.kt: (8, 17): Unresolved reference: td
e: E:\WorkSpace\Berui\Kotlin Koans\Builders\Html builders\src\Task.kt: (9, 21): Unresolved reference: text
e: E:\WorkSpace\Berui\Kotlin Koans\Builders\Html builders\src\Task.kt: (11, 17): Unresolved reference: td
e: E:\WorkSpace\Berui\Kotlin Koans\Builders\Html builders\src\Task.kt: (12, 21): Unresolved reference: text
e: E:\WorkSpace\Berui\Kotlin Koans\Builders\Html builders\src\Task.kt: (15, 28): Unresolved reference: getProducts

These info show in the "Check Details" window When I press 'Check‘ button after I fill code.
How can I resolve this ?

[chuwe1]

FAILURE: Build failed with an exception.

• What went wrong:
  Execution failed for task ':Builders-Html_builders:compileKotlin'.

Compilation error. See log for more details

• Try:
  Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

• Get more help at https://help.gradle.org

BUILD FAILED in 2s

[chuwe1]

My IDE is Android Studio