Code:
\[ \begin{array}{lcl}x_{3}&=&T(x_{2})=7632-2367=5265\\ x_{4}&=&T(x_{3})=6552-2556=3996\\ x_{5}&=&T(x_{4})=9963-3699=6264\\ x_{5}&=&T(x_{5})=6642-2466=4176\\ x_{6}&=&T(x_{6})=7641-1467={\mathbf{6}174}\\ x_{7}&=&T({\mathbf{6}174})={\mathbf{6}174}\end{array} \]