in python 3.6.4

write a gui program that asks the user for three test scores, calculates and displays the average the letter grade according to the grading scale.: if the average score is 90 or more, the person gets an A. 80-89 the person gets a B. 70-79 the person gets a C. 60-69 - the person gets a D. the person fails if the average score is less than 60. the user should be able to enter three test scores, click the button named "calculate average" to calculate and display the average in the window, click the button named "display letter grade" to find and display the letter grade in the window, and click the button named "quit" to close the program. the programs windo should appear as the figure below when it runs:

enter test score: 1 95

enter 2 82

enter 3 90

averag is 89

letter grade is b