Answer:
Step-by-step explanation:
a.
Suppose that "x" is your final exam grade.
Then you want: (87 + 89 + x ) / 3 ≥ 90
(176 + x )/3 ≥ 90
We then multiply the equation by 3 and get
176 + x ≥ 270
Hence x ≥ (270-176)
we get: x ≥ 94
To get A Grade in a course, You must get at least a 94 on the final exam.
b.
If your final average is less than 80, You will lose your B in course
i.e (87 + 89 + x ) / 3 < 80
(176 + x )/3 < 80
We then multiply the equation by 3 and get
176 + x < 240
Hence x < (240-176)
we get: x < 64
You will lose your "B" if your Final grade is less than 64