how to use excel data in matlab

I have about 8 excel of data that i need to incorporate into my code. I need to equal the second column of the files as my y axis. my x axis goes from -20 to +20 in increments of 5. how would I graph these graphs if each graph uses data from three excel files(each file will be only give data for one line in the graph).

I have never used matlab before so please take that into account

[Walter Roberson]

How many graphs do you want to draw? Should the first one be data from files 1, 2, and 3, and the second graph be data from files 4, 5, and 6, and the third graph be data from files 7 and 8?

[me]

the first graph uses three files (3 lines on this graph) the other four graphs use 6 files (3 lines on these graphs as well b/c two of the files have the same x-axis)

[me]

i keep getting the error

Error using xlsread (line 247) File C:\Users\kalkidan\Documents\MATLAB\0deg_30fps.xls not in Microsoft Excel Format.

Error in AeroLab2 (line 11) q_inf0_30 = xlsread('0deg_30fps.xls','0deg_30fps', 'B2');

[Walter Roberson]

Please show some sample lines from the file.