Janey has 3 more than twice the number of books that Sally has. If Janey has 21 books, how many does Sally have?
Define a variable ** Let x be the number of books that Sally has
How many books does Janey have? ** Janey has 3+2x books
Write an equation ** 3+2x=21
Subtract 3 ** 2x=18
Divide by 2 ** x=<<9=9>>9
#### 9