Create an interactive Python script that allows a teacher to enter test scores for their students, calculates each student's mean score and letter grade, and displays a bar chart of the letter grades earned (A - F). Divide your application's work between two functions named input_test_scores and summarize_test_scores. The first function will prompt the user for how many students and how many tests for each student, then use loops to input this data into a 2-d list of student test scores. The function will return this 2-d list of scores.

The second function will accept the 2-d list of test scores as its parameter and calculate the mean test score and associated letter grade for each student. Using this summary data, the function should create and display a bar chart of the letter grade frequencies (in a manner similar to that shown in Section 5.17.2 of the text). Use standard A-F grades as shown in the table below:

Letter Grade | B C D Letter Grades Score score >= 90 90