It is a piece-wise function, so you will have two equations and two different domains. x squared plus 3 represents the sort of parabola and x plus 4 represents a linear function. There is a reason why the point on the parabola is open when x is 4. That open sign means that the x value doesn't work for the equation. Therefore, x cannot be 4 for the parabola and the domain for it is x is less than 4. The point on the linear function is closed to show that 4 for x does work for the equation and graph. For the linear function, the domain for it is x is greater or equal to 4. Hope this helps!
