Jack\textquotesingle s sister is $$22$$ years old, which is $$2$$ less than $$4$$ times Jack\textquotesingle s age. Assume Jack is $$x$$ years old, then． 
Overseas Competition->Knowledge Point->Word Problem Modules->Equation Word Problems
The equation can represents this situation is $$4x-2=22$$,  so, $$4x=24$$, $$x=6$$.  So, the answer is $$6$$. 