Definite Intergrals problem

I'm only posting here because I am not seeing any way to do this in my Text book and my two math help books.

Quote:

Let $\displaystyle \(\displaystyle \int_{10}^{19} f(x) dx =7, \ \int_{10}^{13} f(x) dx=9, \ \int_{16}^{19} f(x)dx =10\)$.

Find $\displaystyle \(\displaystyle \int_{13}^{16} f(x)dx=\)$

and$\displaystyle \(\displaystyle \int_{16}^{13} (7 f(x)- 9)dx=\)$

I'm stuck on the first one.

I'm trying to use the Additive Interval Property as Shown Below.

Quote:

$\displaystyle \mathbf{\int_{a}^{b}f(x) dx= \int_{c}^{a}f(x) dx + \int_{c}^{b}f(x) dx}$

Where a= 13, b=16.

So I try:

Quote:

$\displaystyle \int_{10}^{13} f(x) dx + \int_{16}^{19} f(x)dx $

But keep ending up with the wrong answer, I've resorted by trying different combinations but with no success (even substitution).