15min = 0.25min.

( 100-60)*x+0.25*60=65

The solution is X= 1.25.

60 *1.25+100 *1.25+60 * 0.25 =115 (km)

A: The distance from a:AB to Beijing is 1 15KM.

Solution: Suppose the distance between the car and the valley is x meters when you honk the horn.

72km/h = 20m/s

20×4+340×4=2X

X=720

Answer: When honking the horn, the distance between the car and the valley is 720 meters.

Suppose you need Xs

30X-25X=(240+240+200)-240

Find X=88s.