Write a program that asks the user to enter $4$ test scores. The program should display a letter grade for each score and the average test score.Write the following functions in your program:main$()$: This is where your program input, output, and functions calls to calc$\_$average and determine$\_$grade will reside.calc$\_$average: This function should accept $4$ test scores as arguments and RETURN the average of the scores.determine$\_$grade: This should should accept a test score as an argument and RETURN a letter grade for the score based on the following grading scale:SCORELETTER GRADE$90-100$A$80-89$B$70-79$C$60-69$DBelow $60$FAn example of a running program's output can resemble the following:Welcome to the Grade and Average Calculator.Please enter Test Score #$1$: $66$Please enter Test Score #$2$: $77$Please enter Test Score #$3$: $88$Please enter Test Score #$4$: $95$Test Score #$1$ receives a letter grade of D$.$Test Score #$2$ receives a letter grade of C$.$Test Score #$3$ receives a letter grade of B$.$Test Score #$4$ receives a letter grade of A$.$Your overall test average is: $81\mathrm{.}5$