well the formula for a perimeter of a triangle is 2(lxw) so the length here is 10 i think (just count the cubes on the bottom) then with that number you multiply that by the width (side) then multiply by 2. i counted ten on the length and 5 on the width (im not sure if thats how any because its hard to cound on a tiny grid on a computer hehe), so i multiplied 10 x 5 and got 50, then multiply by 2, i got 100. im not sure, but ill double check :)