According to Hooke's Law, the force required to hold the spring stretchedxm beyond its natural length is given byf(x) =kx, wherekis the spring constant.

Suppose that27J of work is needed to stretch a spring from18cm to24cm and another45J is needed to stretch it from24cmto30cm.Find the exact value ofk, in N/m.

answer: k=______N/m ?

What is the natural length of the spring, in cm?

Answer: ______cm