How much of Brand A fruit punch (10% fruit juice) must be mixed with 4 L of apple juice to create a mixture containing 40% fruit juice?

To find the area, we need to find the height of the triangle. We are given two sides of the small right triangle, where the hypotenuse is also the short side of the obtuse triangle. Find the perimeter of the triangle in Example A. To find the perimeter, we need to find the longest side of the obtuse triangle.
http://www.saylor.org/site/wp-content/uploads/2013/09/K12MATH007-Area-and-Perimeter-of-Triangles.pdf