Final answer:
Sophia needs to earn at least a 92 on her last test to have an 'A' average for the class. Hence the correct answer is option A
Step-by-step explanation:
To calculate the minimum score Sophia needs on her last test to have an 'A' average, we need to find the average of all her test scores.
The sum of her test scores is 91 + 88 + 84 + 92 = 355.
To find the average, we divide the sum by the number of tests: 355 / 4 = 88.75.
To have an 'A' average, she needs a score greater than 90, so the minimum score she must earn on her last test is 92 (option A).