Answer:
Marta need to score at least 94 to receive an average of 90 or higher considering all five tests.
Explanation:
Marks received by Marta in four tests = 86, 84, 97 and 89
Let mark received in fifth test be x
We have average of five test is more than or equal to 90
So we have

So Marta need to score at least 94 to receive an average of 90 or higher considering all five tests.
Answer: The answer should be 4. So it should be written as d = 4. You answer this equation by removing the parentheses, calculating, moving the terms, collect the like terms and calculate some more, then finally divide both sides. Hope this helps!