Answer:
(1.37) AUB = { 1,2,3,4,5,6}
(1.38) AUC = { 1,2,3,4,5 }
(1.39)BUC = { 1,2,3,4,5,6}
(1.40) { 2,4 }
(1.41) { 1,3,5 }
(1.42) { phi }
(1.43) AU(BUC) = { 1,2,3,4,5,6 }
(1.44) { phi }
(1.45) {1,2,3,4,5}
(1.46) { 1,2,3,4,5 }

X is multiple of 9 as well as 12.
Thus, smallest value will be 36 ( 9 *4 = 36, 12 * 3 = 36)
3 and 12 are not the multiples of 9.
72 is a larger multiple than 36; thus, the correct answer is 36.