$4\mathrm{.}2\mathrm{.}1$: Write a method that changes a name so that the last name comes first.

$541666\mathrm{.}3543960.$qx$3$zqy$7$

Write a method lastNameFirst that takes a string containing a name such as "Harry Smith" or "Mary Jane Lee", and that returns the string with the last name first, such as "Smith, Harry" or "Lee, Mary Jane".