Like bought 15 boos six books each cost $7 four of the books each cost $5 the rest of the books each cost $3 how many do all the books cost in all

The total combined cost of 15 books  is $77.

Step-by-step explanation:

Here, the total number of books purchased  = 15

The cost of books = $7 for 6 books

So, the cost of six books  =  6 x ( cost of 1 book) = 6 x ($7)  = $42

⇒Out of 15 books, the cost of 6 books  = $42   (1)

The cost of books = $5 for 4 books

So, the cost offour books  =  4 x ( cost of 1 book) = 4 x ($5)  = $20

⇒Out of 15 books, the cost of 4 books  = $20   (2)

Now, the left books are at cost $3 each book.

The number of left books  = 15 - ( 6+4) = 15 - 10 =  5

So, the cost of books = $3 for 5 books

So, the cost of five books  =  5 x ( cost of 1 book) = 5 x ($3)  = $15

⇒Out of 15 books, the cost of 5 books  = $15   (3)

Now, to get the total price of 15 books add (1) + (2) + (3), we get:

$42 + $20 + $15  = $77

Hence, the total combined cost of 15 books  is $77.