A professor has constructed a two-dimensional array of double numbers having three
rows and five columns. This array currently contains the test grades of the students
in the professor's class. 
Write a Java program that reads 15 array values and then determines:
- the average grade
- the top grade 
- the lowest grade
- the total number of grades in the ranges less than 60, greater than or equal 
to 60 and less than 70, greater than or equal to 70 and less than 80, 
greater than or equal to 80 and less than 90, and greater than or equal to 90.