( 1)58×9 12≈54000(cm)；

54000 cm =540 m.

The school is about 540 meters away from the supermarket.

(2) 102×39≈4000 yuan;

79×39≈3200 yuan.

Answer: He can buy all the basketballs with a unit price of 102 yuan, and it will cost about 3,200 yuan to buy the first basketball.