we know that
∠ECD=∠ACB------> given in the problem
∠DEC=∠CAB------> 90°
so
∠EDC=∠ABC
therefore
triangles EDC and ABC are similar
So
the ratio of the legs are equal
[tex] \frac{x}{9} = \frac{140-x}{81} \\ 81*x=9*(140-x) \\ 81x+9x=1260 \\ 90x=1260 \\ x=14[/tex]
[tex]AC=140-x \\ AC=140-14 \\ AC=126[/tex]
the answer is
AC is equal to 126
