How to find project directory name in Android Studio

$projectDir how can i find this? i'm trying add room dependency in my project `android {

defaultConfig {

    javaCompileOptions {
        annotationProcessorOptions {
            arguments += [
                "room.schemaLocation":"$projectDir/schemas".toString(),
                "room.incremental":"true",
                "room.expandProjection":"true"]
        }
    }
}

}`