I see that you've edited your post after you were asked for clarification. FYI: It is best to post follow-ups and corrections as replies, since edits are usually overlooked.
However, the exercise still does not provide enough information. There is no such thing, as far as I am aware, as a "midpoint" of a triangle. Midpoints are middle points on line segments; they do not refer to any sort of "center" of an area or figure. So "the midpoint of the triangle" has no meaning. Saying that "2x + 8" is "at" the base of the triangle is unclear. Do you mean that this corresponds to some portion of the length of the base, or the entire length of the base, or perhaps the measure of one of the angles at an end of the base, or something else?
Please provide the full and exact statement of the exercise, including the instructions, and giving a detailed description of (or link to) any associated graphic.
Thank you.
Eliz.