Do the following problems without a calculator:

Problem 4.1: 86 + 92 - 86 = ? [Solution]

Problem 4.2: 68/12×(8 + 4) = ? [Solution]

Problem 4.3: 17 - (19×6)/6 + (7 + 19 - 7) = ? [Solution]

Find the number that fits into the question mark.

Problem 4.4: 82 - 19 + ?  = 82 [Solution]

Problem 4.5: (73/?)×14 = 73 [Solution]

Problem 4.6: 12/7×(3 + ?) = 12 [Solution]