Note that the mean (78 +90 +456 +676 + 111+ 381+ 21)/7 = 259
The differences (in absolute value - we're going to square later so it doesn't matter) between each piece of data and the mean are
181, 169, 197, 417, 148, 122, 238
Square each of these and add the results together to obtain 367452
Now your question depends on whether you want the sample standard deviation or population standard deviation - which you have not specified. In the first case divide by 6. In the second case divide by 7. We get roughly 61242 or 52493. The square root of each yields 247.47 or 229.11 depending on whether you want the sample sd or pop sd. The 4 choices imply you are looking for the latter, so the answer is A.i think