a bar magnet whose radius is 20 cm from its center is used to search for an iron pin of the magnetic lines from around the magnets to attract the iron pin is given as 40m webars.

Question

a bar magnet whose radius is 20 cm from its center is used to search for an iron pin of the magnetic lines from around the magnets to attract the iron pin is given as 40m webars. 
determine the magnetic flux density produced by the bar magnet?