Original data: 50,60,70,80,90,100

Suppose that a single additional observation is obtained. If the new average is 47.58, what is the value of the additional observation? (Assume that the new average is calculated using the original data shown above and the new observation).
94.6
98.6
97.6
95.6
96.6

I'm sure you know the formula to find the average; you just sum up all of the data and divide by the total number of observations. The only thing different here is that rather than finding the average of the six numbers you were given, you're going to find the average of seven numbers, six of which you already know and the seventh which is an unknown variable x. You've been told what the new average is, so write out an equation where the left side is the formula for the average of the seven numbers and the right side is the new average, then just solve for x.

(50 + 60 +... + 100 + x)/7 =47.58

Assuming you wrote down the problem correctly, none of those multiple choice answers are even remotely close to the right answer.