line of best fit with range bars

Hi,
I've got pretty basic knowledge of Excel - i want to make a line of best fit with range bars on it. How would i go about doing this? Sorry for being so useless!

I have attached the file im trying to make the graph from.

Thanks
Will

Hi andy - thanks for the reply! sorry i wasnt more specific - for the range bars - i need the smallest and largest plotted and then the mean is what is actually plotted and what the line of best fit uses if you understand me - if not il draw a graph on paper and scan it in!

Thanks!

thats really good but my trend line has to be straight :S

Hi - the data is correct
2 things need sorting though!
- how do i change the horizontal axis round so that the line of best fit goes up from the bottom left to top right?
- the line of best fit has to be straight - it does not go through the data points but calculates its . . . erm. . . position by the means so that on either side it is equal distance - this is explained quite badly. . .

ok - i have kind of got it now - i have added a linear trendline (what i meant by straight line of best fit) but am unable to get rid of the other line. . . still need to switch the axis as well!

-.- damn! i uploaded the wrong excel file. . .
well basically (im not at school anymore so i cant get the chart!) all i did was click add trend line (after right clicking on the line there is already) and added a linear line this leaves the mean lines but adds the linear line i wanted. . . what should i do from here? hang on i can re-download the file and add in the lines

attached the file