In the bike repair shop a lot of flat tires have to be fixed. In the morning the meticulous supervisor is surprised: "All bikes in the repair shop have a flat tire. Three fifths of the front wheels have a flat tire und three fifths of the back wheels have a flat tire. There are 5 bikes with flat tires on both wheels." How many bikes are there in the repair shop today? (A) 15 (B) 20 (C) 25 (D) 30 (E) 35 70 m​