Problem 4: 6!= 720

Problem 7: 1 * 1 * (permutations 8 2) *  (permutations 26 2) = 36400

Problem 10: 26*25*25 = 16250

Problem 12: 5^11= 48828125

Problem 13: 2^15= 32768

Problem 17: 
a) 36^5 = 60466176

b) 36^4 = 1679616


Problem 19: 6^3 = 216

Problem 21: 10 * 26 * 10^4 = 2600000

Problem 22: (26^3  *  10^3)  +  (3  *   26^3 *  10^3) = 70304000

Problem 23: 10^3 * (permutations 3 3) = 6000

Problem 27: (permutations 5 5) = 120

Problem 29: 
a) 2^7 = 128
b) Because someone with 128 keys could open any General Motors car door!

Problem 31: (permutations 6 3) = 120