You can put this solution on YOUR website!
Let's find the sum of her first seven scores, we'll call this y:
Multiply both sides by 7.
Now you want the average of eight test scores to be 90. Lets call the score of the eighth test x, so...
Multiply both sides by 8.
Subtract 581 from both sides.
Flora will need to score 139% on test eight. Not possible!