The common difference is basically the number at which the pattern increases.
A's common difference: 2
B's common difference: 9
C's common difference: 5
answer: A, C, B
Let the number be n.
Then 3n+5 = n+40
Combining like terms, we get
2n = 35, and so n = 35/7, or 17 1/2.
The answer is 3
Multiply 6 by 3 to get the total amount of money for the books then minus the answer 18 which you get from 6 x 3 = 18
Then minus 18 from 21 to get $3
21 - 18 = 3
