Julia spent $60 on a book. the cost of the book was $20 less than twice what she spent on a backpack. how much did the backpack cost? express your answer numerically in dollars. mastering chemistry

If we assume that Jane spent $ x on the black pack 
Then the cost of the book is $ 20 less that twice the cos of the black pack,
Then twice the cost of black pack is 2x, then less $ 20 we get  2x-20
 Hence , 60 =2x-20
           solving for x 
                   x = 40
Therefore, the cost of the black pack is $40.