AndroidSDKToolsException: Unable to resolve build tools directory.

hi. plz some one help me with this trying to get an android apk but as soon as i open build settings i get 3 errors but all are the same thing almost: "AndroidSDKToolsException: Unable to resolve build tools directory. "

ok the problem was the directory of the build tools version that i found in this forum:
link text
before changing: SDK\build-tools\android-9
after : SDK\build-tools\28.0.3\android-9

This just happened with the newest version of Unity (2019.3.5f1) at the time of my answer, but the “build-tools” folder was completely empty and the Build Settings window went dark when I selected Android in the ‘Build Settings’. To resolve this, I just copied the build-tools/28.0.3/ directory from the previous version of Unity into the new version of Unity and everything seems ok.

problem fixed here : Fix Android SDK is outdated | update android sdk unity - YouTube