The boundary line should be solid because it have a 'great/less than or equal to' sign
The answer to your question is option b
To find the other endpoint with a given endpoint and midpoint, you subtract the midpoint values from the endpoint, then with whatever the answer is, you subtract that from the midpoint.
When a straight line is given the form:

m is the gradient. It shows how the value of y changes for an increase of x by 1.
So, in this case, the gradient is
4