The length of a spring is 20cm when a 4kg object is hung. Within the elastic limit, the length of the spring is 1.5cm when the weight of the object is increased by 1kg. Write out the equation of the relationship between the length of the spring y (CM) and the weight of the object x (kg)

The length of a spring is 20cm when a 4kg object is hung. Within the elastic limit, the length of the spring is 1.5cm when the weight of the object is increased by 1kg. Write out the equation of the relationship between the length of the spring y (CM) and the weight of the object x (kg)

Let the original length of the spring be B and the coefficient of elasticity be K. The relation equation between the length L of the spring and the weight F of the object is L-B = KF. According to the meaning of the question, when f = 4, l = 20, so 20-b = 4K; when f = 5, l = 21.5, so 21.5-b = 5K