Final answer:
The value of x that makes a line parallel to b: 3x+13 is x = -5.
Step-by-step explanation:
To find the value of x that makes a line parallel to b: 3x+13, we need to find a line with the same slope. The equation of a line in slope-intercept form is y = mx + c, where m is the slope and c is the y-intercept.
In the given equation, the slope is 3. So, for a line to be parallel, it must also have a slope of 3. This means the correct answer is x = -5, as it will result in a line parallel to b: 3x+13.