First of all, to find the area of a triangle you multiply the base * height and divide the result by two (2).
Let's use a triangle which sides are all 2 inches. To find the area, you do 2*2/2 which equals 2.
Now, double each side and each side of the triangle is now 4.
We do 4*4/2 which now equals 8.
The percentage increase from 2 --> 8 is 600%.
The percentage of the old area to the new area is 800%
ANSWER: 600%