Laura is enrolled in a one semester computer applications class. she achieves grades of 70, 86, 81, and 83 on the first four exams. the final exam counts the same as the four exams already given. if x represents the grade on the final exam, write an expression that represents her course average. if laura’s average is greater than or equal to 80 and less than 90, she will earn a b in the course. write a compound inequality that must be satisfied to earn a b and solve the inequality.