The piece of information that is missing is is the middle line parallel to 2 of the sides. You have to assume it is, otherwise the question is impossible to do.
Givens
The height of the red triangle is 1/2 the top or bottom white triangle. That's because the diagonals and the horizontal line all meet in the middle.
The base of the red triangle is equal to 1/2 the length of the base.
