write a function definition for a function, get_tax taht takes as a parameter an optional tax rate. If the tax rate is not specified, it defaults to 0.1(10%).

The function prompts the user for a purchase amount. If the user enters a vaild number, the function returns the computed tax on that amount. Otherwise the function returns 0.

Not that you do not have to round any value before returning it. Your function musch return the value - not print it.