Since it is an equilateral triangle it means that all the sides are 50. Each side is equal so, if you divide 150 by 3 you get 50. (and since perimeter is the adding of each side)
Now you want to try to figure out what the altitude is of the triangle so you divide it in half. Making the bottom side length now 25 because half of 50 is 25. You now have to use Pythagoreans theorem to figure out the altitude:
