How many engines were built with a cylinder size of 20 ½” x 26”, firebox is belpaire and valve gear is from Stephenson?
create table table_25695027_1 (number_built varchar, valve_gear varchar, cylinder_size varchar, firebox varchar, PRIMARY KEY (number_built))
select number_built from table_25695027_1 where cylinder_size = "20 ½” x 26”" and firebox = "belpaire" and valve_gear = "stephenson"