If it's a triangle that you're talking about, I'm going to guess you need to find the area. Then the equation for finding the area of a triangle is:
1/2*base*height=area
Because a right triangle is basically half a rectangle, so you treat it like a rectangle and multiply the base and the height, and then you cut the answer in half by multiplying by 1/2
_______
I\ I I\
I \ I Multiplying base I \ Dividing the answer by 2,
I \ I And height get you I \ Or multiplying the answer
I \ I this. I \ by 1/2 gets you
I \ I <--- I \ this.
I_____ \I I_____\ <-----
So you need to take the factors that you know and put them into the equation:
1/2*base*height=area
1/2*(b)*(b - 4)=area
If that wasn't what you were looking for, could you specify please?
^_^ I hope this helps!
+10 
