I assume that your triangle is a right triangle.
1. Perimeter. You know already the length of 2 sides. Use Pythagorean theorem to find the 3rd side:
Thus the perimeter is p = 20 + 16 + 12 = 48
2. Area: The area of a right triangle is the half of a rectangle. The sides of the rectangle are the legs of the right angle. Thus
Therefore the area of the triangle is 96 square units.