Answer
$(6,-3)$ and $(-2,-3)$
Work Step by Step
If the major axis is parallel to the x-axis, then the y-coordinates of the foci will be the same as the y-coordinate of the centre. We can get the two foci's x-coordiantes by adding and substracting the given $a$-value from the centre's x-coordinate. Hence the $2$ foci:
$(2+a,-3)=(2+4,-3)=(6,-3)$ and $(2-a,-3)=(2-4,-3)=(-2,-3)$
