Hey there!
The answer to your question is 94.5
We can use this equation, and solve: (we need to use "2x" because the score counts for 2 grades!)
(89 + 79 + 93 + 2x) / 5 = 90
(261 + 2x) / 5 = 90
261 + 2x = 450
2x = 189
x = 94.5
To check if it's right, we can add up all the scores, and divide by 5, and see if it's equal to 90. (Make sure to use 94.5 twice because it counts for 2 test grades!)
(89 + 79 + 93 + 94.5 + 94.5) / 5
450 / 5
90 ✔️
Hope it helps! Have a great day and good luck!