How many {capital of} are to/by {Achaemenid Empire} ?
What is the number of cities in the Archaemenid Empire?
How many cities are in the Archaemenid Empire?
SELECT ( COUNT ( ?s ) AS ?u ) { ?s property:capital_of resource:Achaemenid_Empire }
SELECT (COUNT(?sub) AS ?subs ) {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> ?sub .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate> <http://www.wikidata.org/entity/P1376> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> http://wikidata.dbpedia.org/resource/Q389688 .
} 

SELECT (COUNT(?sub) AS ?value ) { ?sub wdt:P1376 wd:Q389688 }
4