Define a function find$\_$employee$\_$tax$()$ that takes one parameter as a person's age, and returns the person's tax percent. The tax percent is returned as follows:

If the person's age is less than $20$ years old, then the tax percent is $0\mathrm{.}38.$

If the person's age is between $20$ and $40$ years old inclusive, then the tax percent is $0\mathrm{.}25.$

Otherwise, the tax percent is $0\mathrm{.}18.$