(2)30-20= 10 (minutes).
So Xiaogang stayed in the book city for 10 minutes;
(3) Xiaogang's journey from Book City to Children's Palace is 6250-4000=2250 meters, and it takes 35-30=5 minutes.
The riding speed of Xiaogang from Book City to Children's Palace is 2250 ÷ 5 = 450 (m/min);
(4) 6000++= 6000+2000+2250 =10250 (m).
A: From home to the Children's Palace, Xiaogang rides a bike 10250 meters.