A.

cannot be the power set of any set. Consult Cantor's theorem, which says that the cardinality of the power set of any set (even the empty set) is strictly greater than the cardinality of the set.
(No part b?)
c. Also not the power set of any set, because any power set must have

elements, where

is the cardinality of the original set. The cardinality of this set is 3, but there is no integer

such that

. This set would be a power set if

(that is, the set containing the empty set) were a member of it.
<span> the answers are B and D
hope this helps out :}</span>
The cost of an adult ticket is £6 more than that of a child ticket, so will be denoted by c+6. Now, we are told that the cost of four child tickets and two adult tickets is £40.50, so we can put this in an equation and solve for c:
(c+6)+(c+6)+c+c+c+c=40.50
6c+12=40.50
6c=28.50
c=4.75
Therefore the cost of a child's ticket (c) is £4.75 and the cost of an adult ticket (c+6) is £10.75.
Benchmark are numbers that are used as standards to which the rest of the data is compared to. When counting numbers using a number line, the benchmark numbers are the intervals written on the axis. For benchmark numbers of 10, the number line on top of the attached picture is shown. Starting from 170, the tick marks are added by 10, such that the next numbers are 180, 190, 200, and so on and so forth. When you want to find 410, just find the benchmark number 410.
The same applies to benchmark numbers in intervals of 100. If you want to find 170, used the benchmark numbers 100 and 200. Then, you estimate at which point represents 170. For 410, you base on the benchmark numbers 400 and 500.