What is the number for the moment of intertia in torsion (j) (cm 4) for the 4.7 web thickness (mm)?
create table table_2071644_1 (moment_of_inertia_in_torsion__j___cm_4__ varchar, web_thickness__mm_ varchar, PRIMARY KEY (moment_of_inertia_in_torsion__j___cm_4__))
select count(moment_of_inertia_in_torsion__j___cm_4__) from table_2071644_1 where web_thickness__mm_ = "4.7"