The same card is on Ancestry.com
The card is explained on Ancestry: Arrival Date is June 13, 1930.
Another card on Ancestry indicates his naturalization took place at the Princeton Ill. Circuit Court, Bureau County Ill.
The records are not indexed on FamilySearch, but the images themselves have an alphabetical index on the first few pages
Jacob Brostoff's Declaration is record #1459, image #42 in this set.
His Petition is record #759, image #161 in this set. This matches P-759 on the Ancestry Index card.