Step 1 :\(1 + 3 + 4 + 6 + 6 + 3 = \boxed{23}\)
Step 2 :\(20 - 12 = 8\), \(8 + 1 = \boxed{9}\)
Step 3 :\((21 + 29) / 2 = \boxed{25}\)
Step 4 :The modal class is the class with the highest frequency. In this case, there are two classes with the highest frequency of 6, which are 39-47 and 48-56.
Step 5 :\(65 + 1 = 66\), \(66 + 9 - 1 = \boxed{74}\)