so easy
so driscoll has 9 reports to grade and each page has 6 pages.
just multiply 9 and 6 which gives you your answer 54.
so out of 54, he has graded only 12 pages which means that you need to subtract.

driscoll has 42 pages left to grade.
you can recheck your answer by adding 42 ans 12 which gives your answer as 54. so yup our answer is right.