For a, since a straight line is 180 degrees, that means that x+x+35=180. Subtracting 35 from both sides, we get 145=2x. Next, we can divide both sides by 2 to get 72.5=x
For b, since vertical angles (opposite angles from intersecting lines) are equal, that means that 3x+13=5x-3. Subtracting 3x from both sides as well as adding 3, we get 2x=16. Dividing both sides by 2, we get x=8