CREATE TABLE table_28016 ("Class" CLOB, "Firebox" CLOB, "Cylinder size" CLOB, "Valves" CLOB, "Valve gear" CLOB, "Number built" CLOB, "Years built" CLOB)

How many engines were built with a cylinder size of 20 x 26 , firebox is belpaire and valve gear is from Stephenson?
SELECT "Number built" FROM table_28016 WHERE "Cylinder size" = '20 ½” x 26”' AND "Firebox" = 'Belpaire' AND "Valve gear" = 'Stephenson'
SELECT "Number built" FROM "table_28016" WHERE "Cylinder size" = '20 ½” x 26”' AND "Firebox" = 'Belpaire' AND "Valve gear" = 'Stephenson'