We have been given a piece wise function in which one graph is of parabola and other one is of a straight line.
When we shift the graph of
above by 6 units then the equation of the graph is
.
Since, the given graph of the parabola full fills this criteria. Hence, the equation of the parabola is given by

The graph of the parabola is up to x=3. At point x=3 there is an open circle. Hence, we must include less than sign.
Now, the equation of the line is given by

We have a solid sign , hence we must include greater than equal to sign.
Therefore, the equation for the piece wise function is given by

C is the correct option.