So let's imagine that the base of the triangle is x, and since the height is 13 less, the height will be x-13. So since the formula for area is base*height/2, plug x(x-13)/2=24, which is the area, and solve. You would get x^2-13x=48, and bring the 48 to the other side to get x^2-13x-48=0. Through the quadratic formula, you would get x=16 and x=-3. Since -3 cannot be valid for a triangle, 16 is the answer.
Midsegment of a Triangle Theorem - is the right choice
<em>The Midsegment Theorem states that the segment connecting the midpoints of two sides of a triangle is parallel to the third side and half as long.</em>