Android build fails every time : tried all versions of build tools and fixes. plz help

Hello,
I am using unity 2017.3.0f3 personal on win 8.1 machine. using jdk 1.7.0_79 and build tools 26. when i build on android i i shows gradle build failed. with following errors -

1--- CommandInvokationFailure: Gradle build failed.
C:/Program Files/Java/jdk1.7.0_79\bin\java.exe -classpath "C:\Program Files\Unity\Editor\Data\PlaybackEngines

\AndroidPlayer\Tools\gradle\lib\gradle-launcher-4.0.1.jar" org.gradle.launcher.GradleMain "-Dorg.gradle.jvmargs=-Xmx2048m" "assembleRelease"

stderr[

FAILURE: Build

failed with an exception.

* Where:
Build file 'C:\Users\LENOVO PC\Documents\newtry\Temp\gradleOut\build.gradle' line: 20


2------Build completed with a result of 'Failed'
UnityEngine.GUIUtilityrocessEvent(Int32, IntPtr)



3-----UnityEditor.BuildPlayerWindow+BuildMethodException: 3 errors
at UnityEditor.BuildPlayerWindow+DefaultBuildMethods.BuildPlayer (BuildPlayerOptions options) [0x0020e] in C:\buildslave\unity\build\Editor\Mono

\BuildPlayerWindowBuildMethods.cs:181
at UnityEditor.BuildPlayerWindow.CallBuildMethods (Boolean askForBuildLocation, BuildOptions defaultBuildOptions) [0x00065] in C:\buildslave\unity\build\Editor\Mono

\BuildPlayerWindowBuildMethods.cs:88
UnityEngine.GUIUtilityrocessEvent(Int32, IntPtr)


I found some fixed on unity answers. i changed build tools to 23 then 21 but nothing happend. I tried reimporting all assets but no results. then i updated my whole android sdk still no result.

I even tried a simple unity project with minimal assets and objects and tried to build it. but still same errors.

now i cant understand what to do. Plz help.

 

If you want this problem solved in a timely manner, it'd be best if you posted it in the correct forum. https://forum.unity.com/forums/android.30/