public static Task<double> AverageAsync<TSource>(
	this IQueryable<TSource> source,
	Expression<Func<TSource, long>> selector,
	CancellationToken cancellationToken
)

<ExtensionAttribute>
Public Shared Function AverageAsync(Of TSource) ( 
	source As IQueryable(Of TSource),
	selector As Expression(Of Func(Of TSource, Long)),
	cancellationToken As CancellationToken
) As Task(Of Double)