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.