area of a triangle with the base and height

[S.Hobden]

Write an expression in simplest form for the area of a triangle with a base of (1/x^2-4x-21) , and a height of ( x + 3).

ok...so, i know that that the area of a triangle is
bh/2
and i know i first have to find the sides using the hight, but i forget how to do that, and the x's always confuse me.

 

[pka]

\(\displaystyle \L
\frac{1}{2}bh\quad \Rightarrow \quad \frac{1}{2}\left( {x + 3} \right)\left( {\frac{1}{{x^2 - 4x - 21}}} \right)\)

Factor! Reduce.