The answer is 144.
AC and CE have the same ratio as BA and DE. So you can get the answer by getting their proportions.
84 = 7
156-x x
Cross multiply, transpose, and simplify to get the variable x.
84x = 1092-7x
84x + 7x = 1092
91x = 1092
x = 12
To get AC, substitute.
AC = 156 - x
AC = 156 - 12
AC = 144
