Answer:
She needs to get at least 96 on the 4th test to earn an average of at least 90 in the class.
Explanation:
(97+78+89+?) divided by 4 at\geq 90
It is divided by 4 because it is the average of 4 test scores.
To Solve: (97+78+89+?) divided by 4 at\geq 90
Multiply by 4 on both sides 97+78+89+? at\geq 360
Isolate variable: ? at\geq 96