Gradle Project Sync Failed - Android Studio

Question

I have been working on an android app through android studio for about a month now. I recently got a new computer, and tried to open the app files on that computer. When I open it I get an error banner saying

Gradle Project Sync Failed. Basic functionality (e.g. editing, debugging) will not work properly.

When I click the try again button the error in the console reads the following:

Error:failed to find target android-21 : C:\Users\compu\AppData\Local\Android\sdk Install missing platform(s) and sync project

I don't have access to the computer I created this project on. Is there a simple way to fix this?

Solution

Try launching SDK Manager from AndroidStudio's menu icon then install Android 21 packages.