One-score of men is 20 men, so two-score would be forty. :)
1,2,7,10,10
The "mean", or "mean average" in full, is obtained by adding up all the numbers and then dividing by the number of numbers there are. It is saying that if the numbers were all the same, this is what they would be.
Mean is the average of numbers. For example, if you were trying to get the mean of 24 and 12, you would first add the numbers (which is 36) and you divide them by how many numbers are in the problem (which is 2). So the answer would be 18.
Since score is defined as 20, 4 score is 80. I am assuming by 4 score you mean 4 score years (as opposed to 4 score seconds, minutes, etc.). Since 4 score is 80, 4 score years is 80 years.