The only solution is (-3/2, 4)
read my attachment
X is equal to 22.25 so all you have to do is to fill it in and find the answers
We add up all those numbers (excluding 30) and divide by the number of numbers (9). This results in 78.8 (round up to 79).
79-74 = 5. So the mean has increased by 5 points. (C)