From the figure, we have the following coordinates of the vertices :

a. Rotation of 180 degrees about the origin has a rule of :

The sign of the coordinates will change from positive to negative or negative to positive.
The new coordinates will be :

The graph will be :
b. Reflection across the x-axis has a rule of :

Only the y coordinate will change its sign.
So from the coordinates we got in a.

The graph will be :