Can someone help me with this confidence intervals for the mean sigma known?

Can someone help me with this confidence intervals for the mean sigma known? I don't understand.

The formula is E= zsubc * sigma / sqrt n

Assuming .05 as your alpha value, make up a problem similar to this one. Make up 36 gas prices for your example. Use price values in your list that some you made up and be sure they are similar to the prices you have had in your area.