How do I calculate this question? find the position of the centre of gravity in %
I believe that the Length of the Aerodynamic Chord is $19\ m - 13\ m = 6\ m$, and that the CG is $2 m$ from the Leading Edge of the Mean Chord (LEMC).

Therefore, I believe that the CG in percent is:
$$
\mathrm{\frac{CG}{Length\ of\ Chord}} = \frac{CG - LEMC}{TEMC - LEMC} = \frac{15-13}{19-13} = \frac{2}{6} = 33\%
$$