Answer:
A score between 79 to 100
Step-by-step explanation:
As the average is not a simple number but a range between 79 and 86 you need to make a decision on what average number to choose, for example we can choose the 79 or 86
First we choose 79
Then (test1+test2+test3)/3=79
(75+83+test3)/3=79
75+83+test3=237
Test3=237-75-83
Test3=79
Second we choose 86
(test1+test2+test3)/3=86
(75+83+test3)/3=86
75+83+test3=258
Test3=258-75-83
Test3=100
According to this you need a score in the range from 79 to 100 to have a test average between 79 to 86
