diff --git a/build.gradle b/build.gradle
index 0d54c35..00016e7 100644
--- a/build.gradle
+++ b/build.gradle
@@ -1,13 +1,21 @@
 plugins {
-    id 'org.jetbrains.kotlin.jvm' version '2.2.10'
+    id 'org.jetbrains.kotlin.jvm' version '2.0.21'
 }
 
 test {
     useJUnitPlatform()
 }
 
+java {
+    sourceCompatibility = JavaVersion.VERSION_21
+    targetCompatibility = JavaVersion.VERSION_21
+    toolchain {
+        languageVersion = JavaLanguageVersion.of(21)
+    }
+}
+
 kotlin {
-    jvmToolchain(17)
+    jvmToolchain(21)
 }
 
 group 'ru.otus'
@@ -18,6 +26,7 @@ repositories {
 }
 
 dependencies {
-    implementation "org.jetbrains.kotlin:kotlin-stdlib"
+
+    implementation("org.jetbrains.kotlin:kotlin-stdlib:2.0.21")
     implementation 'org.junit.jupiter:junit-jupiter:5.8.1'
 }
\ No newline at end of file
diff --git a/src/main/kotlin/ru/otus/homework/home_work.kt b/src/main/kotlin/ru/otus/homework/home_work.kt
new file mode 100644
index 0000000..81f2487
--- /dev/null
+++ b/src/main/kotlin/ru/otus/homework/home_work.kt
@@ -0,0 +1,34 @@
+package ru.otus.homework
+
+fun main() {
+    println(sumAll(null, null))
+    println(concatAll("arg1", "arg2", "arg3", separator = '+'))
+    println("duration is ${duration { Thread.sleep(1100) }}")
+}
+
+// ## 1. Функция с обязательными и необязательными позиционными параметрами
+internal fun sumAll(field1: Int?, field2: Int?, vararg fields: Int?): Int {
+    var sum: Int = (field1 ?: 0) + (field2 ?: 0)
+    for(field in fields){
+        sum += (field ?: 0)
+    }
+
+    return sum
+}
+
+//## 2. Функция с необязательным параметром и позиционными параметрами
+internal fun concatAll(vararg args: String, separator: Char = ' ') : String {
+    var concatenation = ""
+    args.forEach { v -> concatenation += v + separator.toString() }
+
+    return concatenation.substring(0, concatenation.length - 1)
+}
+
+//## 4. Функция, измеряющая время выполнения другой функции
+fun duration( callback: () -> Unit): Long {
+    val before = System.currentTimeMillis()
+    callback()
+    val after = System.currentTimeMillis()
+
+    return after - before
+}
\ No newline at end of file
diff --git a/src/test/kotlin/ru/otus/homework/FunctionsTest.kt b/src/test/kotlin/ru/otus/homework/FunctionsTest.kt
index 93a36cf..137849d 100644
--- a/src/test/kotlin/ru/otus/homework/FunctionsTest.kt
+++ b/src/test/kotlin/ru/otus/homework/FunctionsTest.kt
@@ -1,6 +1,7 @@
 package ru.otus.homework
 
 import org.junit.jupiter.api.Assertions
+import org.junit.jupiter.api.DisplayName
 import org.junit.jupiter.api.Test
 
 class FunctionsTest {
@@ -11,4 +12,11 @@ class FunctionsTest {
             calculate(1, 2)
         )
     }
+
+    @Test
+    @DisplayName("## 3. Тестовая функция для пункта №2")
+    fun concatenationVarargsBySeparatorTest(){
+        Assertions.assertEquals("str1 str2 str3", concatAll("str1", "str2", "str3"))
+        Assertions.assertEquals("str1,str2,str3", concatAll("str1", "str2", "str3", separator = ','))
+    }
 }
\ No newline at end of file