The Marks obtained ( out of 20) by 30 students of class in a test are as follows : 14,16,15,11,15,14,13,16,8,10,7,11,18,15,14,19,20,7,10,13,12,14,15,13,16,17,14,11,10,20. Prepare a frequency distribution table for the above data using class intervals of equal width in which one class interval is 4−8 ( excluding 8 and including 4).