A black triangle has a base length of x. It is known that when the lenth of the base has 1 added and is then doubled this is the same as the height of the triangle.

A small white triangle has an area of 9-x. It is placed in the middle of the black triangle. A red triangle is then made with the same area of the black left showing. The red triangle has an base length of x-3 find its hieght