Need help ASAP, stuck on this question

Answer:
a = 12+6(n-1) (BOTTOM LEFT)
Step-by-step explanation:
a = x + y(n-1)
x = the original amount; y = amount it increases by
a = 12+6(n-1)
Answer:
12 + (n-1)*6
Step-by-step explanation:
The first book costs 12 dollars
The next book and each additional book costs 6 dollars
Let n the the number of books
The first book is 12, so we multiply by 1 less book for the 6 dollar books,
or n-1
The cost for all the books is 12 + (n-1)*6