Answer: 7.142857 or 7 1/7
Step-by-step explanation:
a. A' means the complement with respect to Z? If so, then
To know A' you need to write all the elements in Z that are not in A.

b. All the subsets of B, is knowed as P(B),

c.
(Add to A the elements of B, or equivalently add to B the elements of A)
d.
express informally speaking the elements that have in common, but there is no element in common, so

A is congruent to X
B is congruent to Z
C is congruent to Y
AB is congruent to XZ
AC is congruent to XY
BC is congruent to ZY
ABC is congruent to XZY
2383x28393=18283 that is the correct
He started at the wrong end of the number.
He should have started with the 3-8 and borrowed ending up with 85