Which is the value of this expression when a=5 and k=-2

Reading tests are compared for two students. sara got 98, 100, 65, 78, 98, 46, 100, 100, 45, and 50 on her reading test. lee got 97, 67, 89, 99, 100, 45, 79, 89, 58, and 67 on his reading test.