Acrobats walk a tightrope on a unicycle. The diameter of the wheel is 40 cm. How many turns does a 50-meter-long steel cable take?
The range of the automatic rotary sprinkler irrigation device on the park lawn is 9M, what is the area it can spray irrigation?
4 Xiaodong measures the circumference of the thickest part of a tree trunk as 125.6cm, and what is the cross-sectional area of the thickest part of the trunk?