The mean, median, and mode of the $7$ data values $60,100, x, 40,50,200,90$ are all equal to $x$. What is the value of $x$? (2016 AMC 10A Problems, Question \#7) 
选项为:A:$$50$$  B:$$60$$  C:$$75$$  D:$$90$$  E:$$100$$  请回答其中一个选项.