\(\because\) '-4' is root of equation x2 + mx - 4 = 0
\(\Rightarrow\) 16 - 4m -4 = 0 \(\Rightarrow\) 4m = 12 \(\Rightarrow\) m =3
Now,
x2 + mx + a = 0 \(\Rightarrow\) x2 + 3x + a = 0
has equal roots
Then, b2 - 4ac = 0
\(\Rightarrow\) 9 - 4a = 0
\(\Rightarrow\) 4a = 9