Subtract $\sqrt { - 81 } - \sqrt { - 4 }$

Multiple Choice

Subtract $\sqrt { - 81 } - \sqrt { - 4 }$ and write in standard form.

A) $22 i$
B) $11 i$
C) $\sqrt { - 7 } i$
D) $7 i$
E) $- 7 i$