The johnson family drove to the mountains for a vacation. mr. johnson drove x miles. mrs. johnson drove 2 times the number of miles that mr. johnson did. if the johnsons drove 330 miles, how many miles did mrs. johnson drive?

220 miles is how much Mrs. Johnson drove. because . . .

2x+x=330
2x is twice the amount of Mr. Johnson which equals Mrs. Johnson.
The plain "x" is how much Mr. Johnson drove. 

2x+x= 3x
3x=330- x=110

If 'x' is how much Mr. Johnson drove then we multiply that by two to get 220.