For this case we have that by definition, a flat angle is the space included in an intersection between two straight lines whose opening measures 180 degrees.
Now, according to the figure we have that from V to S there are 180 degrees, like this:
![5x + 25x + 30 = 180](https://img.qammunity.org/2020/formulas/mathematics/middle-school/ch1u4ggdsls375ev9o47ydda7g1wdi7s5w.png)
We add similar terms:
![30x + 30 = 180](https://img.qammunity.org/2020/formulas/mathematics/middle-school/nd1remru2yzayhzejeclfw07y5z6s1mg2z.png)
Subtracting 30 from both sides of the equation:
![30x = 150](https://img.qammunity.org/2020/formulas/mathematics/middle-school/bdxtdzta0xdf4o16201zd8o30qwj56ozug.png)
Divide by 30 on both sides of the equation:
![x = \frac {150} {30}\\x = 5](https://img.qammunity.org/2020/formulas/mathematics/middle-school/8lccega84mlnkam3m5sqrgyo2zyqi0dmo1.png)
Answer:
![x = 5](https://img.qammunity.org/2020/formulas/mathematics/high-school/q47q2r4ttysyvhwrvmu4tvjt4greotllkp.png)