We have a triangle with its medians AE, FB, and CD. The medians intersect at point O, which is called the centroid of the triangle.
The centroid is always 2/3 of the length of the median from each vertex.
Therefore if AE = 21, then AO must be 2/3 of that.
[tex]\begin{gathered} AO=\frac{2}{3}AE \\ \\ AO=\frac{2}{3}(21) \\ \\ AO=14 \end{gathered}[/tex]
The answer is option A, 14.
