Question: Dutch Mathbook is at it again

Hello everbody! 

Ive got a question about my dutch math book, and why it thinks its answer is better than mine. 

It is question c. the integral that is covers the x value from 4 to 6 for f(x). 

I would think that means the integral of 1 to 6 - the integral of 1-4, and thus 4-7=-3. Now i dont know how they thought about getting a smaller area under the function with a larger domain of x, so i am not sure what is going on. Im not even sure if what they ask is possible. The book gave 3 as an answer. My answer was -3. Looking at it, and thinking about it. It may not even be possible. 

Any way, that is the question. 

Picture 2 shows the rules, picture 3 shows the answers of the book. 

Thank you!

Greetings,

The function

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