7+4-5+21-2+4=29 Then I used football knowledge to find that they started on the other teams 28 yard line :)
The formula for the standard error is this:
σM = σ / √N
where
σM is the standard error
σ is the standard deviation
N is the number of samples
So,
σM = 0.45 / √50
σM = 0.0636 or 6.36%
The standard error is 0.0636