On Monday, Mrs. Watson grades 120 x 60% = <<120*60*.01=72>>72 final exams.
At the end of Monday, she has 120 - 72 = <<120-72=48>>48 exams left to grade.
On Tuesday, she grades 48 x 75% = <<48*75*.01=36>>36 final exams.
On Wednesday, she has 48 - 36 = <<48-36=12>>12 exams left to grade.
#### 12