On Tuesdays, Mr. Cansetti walks from his home, located at one end of Main Street, to the grocery store at the other end of Main Street. On his way down Main Street, he passes the post office and the police station, in that order. Mr. Cansetti's home is 7.5 blocks from to the police station. The post office is 6 blocks from the grocery store and 3.5 blocks from the police station. How many blocks does Mr. Cansetti walk from his home to the grocery store?