How many {powerplant} are to/by {two-stroke engine} ?
What is the number of power plants that use two-stroke engines?
How many power plants use two-stroke engines?
SELECT ( COUNT ( ?g ) AS ?q ) { ?g property:powered_by resource:two-stroke_engine }
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/P516> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> http://wikidata.dbpedia.org/resource/Q152323 .
} 

SELECT (COUNT(?sub) AS ?value ) { ?sub wdt:P516 wd:Q152323 }
26