Answer:

And the best answer on this case would be:
b) m = 4.635
Step-by-step explanation:
Let X the random variable of interest and we know that the confidence interval for the population mean
is given by this formula:

The confidence level on this case is 0.9 and the significance 
The confidence interval calculated on this case is 
The margin of error for this confidence interval is given by:

Since the confidence interval is symmetrical we can estimate the margin of error with the following formula:

Where Upper and Lower represent the bounds for the confidence interval calculated and replacing we got:

And the best answer on this case would be:
b) m = 4.635