I did the problem myself and my teacher always said thatif you don't get the exact answer then round to the closest one. The answer that i got was 31,808.6, the closest one to that would be letter C.
Answer:

Step-by-step explanation:
-The margin of error is calculated using the formula:

-We substitute the values, n=900 and ME=30 in the formula to solve for standard deviation:

Hence, the population standard deviation is 547.1125
1/10 = 0.1
0.9 x 0.1 = 0.09
0.09 is your answer
hope this helps