=30

Number of people boarding at the starting point (first stop), 9 stops in the middle and the last stop (*** 10 stop). So it starts with 10 people.

Similarly, at the second stop, 9 people got on and 1 got off.

At the third stop, eight people got on the bus and two people got off.

......

At the fourteenth stop, 1 people get on and 9 people get off.

At the fifteenth stop, no one got on, and 10 got off.

Fewer people get on the bus and more people get off.

Reach the maximum at the fifth stop.

(10+9+8+7+6)-(0+1+2+3+4) = 30 (pieces)