def METHOD_NAME(platform_arn):
    """
    Method determines the EB-managed solution stack represented by a PlatformArn
    :param platform_arn: PlatformArn of a solution stack
    :return: SolutionStack representing the PlatformArn if it an EB-managed platform, otherwise None
    """
    if not PlatformVersion.is_eb_managed_platform_arn(platform_arn):
        return
    platform_description = elasticbeanstalk.describe_platform_version(platform_arn)
    return SolutionStack(platform_description['SolutionStackName'])