Determine the Values of a and B That Satisfy the Equation

Multiple Choice

Determine the values of a and b that satisfy the equation. $$\sqrt { - 81 } - 7 = a + b i$$

A) $a = 14 ; b = 18$
B) $a = 49 ; b = - 9$
C) $a = 81 ; b = - 7$
D) $a = - 9 ; b = 7$
E) $a = - 7 ; b = 9$