Do you know the area of a trapezoid? Look hereI am trying to understand how to solve this problem. Area of a trapezoid inside of a triangle.
For more on midlines (or midsegments), see https://mathbitsnotebook.com/Geometry/SegmentsAnglesTriangles/SATMidSegments.html.
The same similar triangles that prove that theorem are useful for a lot of other things, so they're worth being aware of. (I deliberately used the term so you might search for it and learn about the theorem, though it wasn't essential.