求助：F2的 index 一道习题

题目：Four years ago material X cost$5 per kg and the price index most appropriate to the cost of material X stood at 150.
The same index now stands at 430.
What is the best estimate of the current cost of material X per kg？

答案：$14.33($5*430/150)

这题具体步骤是什么？怎么做的？