Answer:
$10
Step-by-step explanation:
The hardcover books are $12 each which would be $60 out of the $100. There are four more paperbacks meaning they would be $10 each and cost $40 total.
I hope this helped!!! :)
The way I figured this one out was saying that if it takes 2lbs to stretch it to 12 inches and 5lbs to stretch to 18 inches that means that 3 additional pounds = 6 inches. Therefore, each additional pound is 2 inches. We know already that with 2 lbs it was 12 inches in length and we can also say that 2 lbs = 4 inches. So subtract 4 from 12 and you end up with the answer of 8 inches.

We know that,
- Pythagoras theoram is given by : p² + b² = h²
- In a Pythagoras triplet, the longest side represents the hypotenuse of the triangle.
Then,
We should check that, whether the sum of squares of the smaller sides will be equal to the square of the third side or not. Then, we can determine the above easily.
Sum of squares of smaller sides:
= 6² + 8²
= 36 + 64
= 100
Square of longer side:
= 10²
= 100
Sum of squares of smaller sides = Square of longer side. Hence, 6,8,10 are Pythagorean triplets.
And we are done! :D
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