The surface area of a cylinder is equal to the area of a rectangle. The length of the rectangle is equal to the circumference of the bottom of the cylinder. It is known that the area of the rectangle is 131.88 square centimeters, and the height of the cylinder is 4 cm. What is the radius of the bottom of the cylinder?
一个圆柱体的表面积和一个长方形的面积相等．长方形的长等于圆柱体的底面周长，已知长方形的面积为131.88平方厘米，圆柱体的高是4厘米，圆柱体的底面半径是多少？
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