Hello Anna,
First, you'd want to find out how many papers Morgan has graded after 7 hours: 9 per hour, so in 7 hours, it would be 7 * 9 = 63 papers
Morgan took 87 papers home to grade. After working for 7 hours, she graded 63 of them.
You can now figure out how many papers she has not yet graded yet by subtracting the two numbers in bold.