Answer:Sally read 68 pages last week.
Explanation:
Let x represent the number of pages that Sally read last week. The book has a total of 590 pages. She already read some of it last week.
She plans to read 50 pages tomorrow and by then, she will be 1/5 of the way through the book. This means that the total number of pages that she would have read by tomorrow would be
1/5 × 590 = 118
It means that the sum of the number of pages that she read last week and the 50 pages that she planned to read tomorrow is 118. Therefore
50 + x = 118
x = 118 - 50 = 68