4. Create a function `clicker-grades`, that consumes two lists of symbols of equal length. Each symbol
will be one of 'a', 'b', 'c', 'd', or 'e'. The first list, `corr-answers`, contains the correct answers to the
clicker questions. The second list, `stu-answers`, contains a student's answers to the clicker
questions. You may assume that the first element of `corr-answers` corresponds to the first element
of `stu-answers`, and so on. `clicker-grades` produces the number of correct responses the student
gave.
For example:
(clicker-grades (list 'a 'a 'b 'c) (list 'a 'd 'b 'd)) => 2