Factor Completely $5 a ^ { 2 } - 16 a - 45$

Multiple Choice

Factor completely. $5 a ^ { 2 } - 16 a - 45$

A) $( 5 a - 45 ) ( a + 1 )$
B) $( 5 a + 9 ) ( a - 5 )$
C) $( 5 a - 9 ) ( a + 5 )$
D) $( 5 a - 1 ) ( a + 45 )$
E) Not factorable