For What Value Of $a$ Does the Equation $x ^ { 2 } + y ^ { 2 } - a x + 6 y + 33 = 0$

Multiple Choice

For what value of $a$ does the equation $x ^ { 2 } + y ^ { 2 } - a x + 6 y + 33 = 0$ represent a circle with center $( 7 , - 3 )$ ? When $a$ assumes this value, what is the radius of the circle?

A) $\quad a = 14$ , radius $= 5$
B) $\quad a = 13 , \quad$ radius $= 4$
C) $\quad a = 13$ , radius $= 6$
D) $\quad a = 15 , \quad$ radius $= 7$
E) $\quad a = 12 , \quad$ radius $= 6$