Answer:
[tex]a2 + 5a + 4 \: \: when \: a = 3 \\ = (3)2 + 5(3) + 4 \\ \\ = 6 + 15 + 4 \\ = 25[/tex]
[tex]a2 - 5a \: \: when \: a = 3 \\ = (3)2 - 5(3) \\ = 6 - 15 \\ = - 9[/tex]
