Answer:
11
Step-by-step explanation:
average = sum / count
count = 3 (there are three trials)
average = 9
9 = sum / 3
sum = first score + second score + third score
= 6 + 10 + third score
9 = (6+10+third score)/3
multiply both sides by 3 to remove the denominator
27 = 6 + 10 + third score
= 16 + third score
subtract 16 from both sides to isolate the third score
11 = third score
