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In the fourth grade of primary school, Peking University Green Card (Beijing Normal University Edition), Volume II, Mathematical Problems [Setting Equations to Solve Applied Problems (Also Write)]
Let the width of a rectangle be x cm.

(x+2x)*2=30

x=5

5cm in width and 10cm in length.

The area is 10*5=50 square centimeters.

Set a small passenger plane to fly x meters per hour.

4x-320= 1080

4x= 1400

x=350

A: The speed of the passenger plane is 350 kilometers per hour, which is 350,000 meters.

Suppose xiaoxiao is x years old.

x+27=4x

3x=27

x=9

4*9=36

A Xiaoxiao is 9 years old and her mother is 36 years old.

Suppose b travels x kilometers per hour.

20x-36*20=50

20x=770

x=38.5

Answer B: The speed is 38.5 kilometers per hour.