plotting a data file in ginuplot in linux

I don't know if this is the correct place for this, but I wanted to graph in gnuplot one column of a data file using the formula y=mx+b... where m is a constant and b is a constant...x is the data and y is unknown. I known how to move that one column of data to its own file and that's what I have done. I need a code for the mx+b graph though...I obviously know how to apply that formula but I don't know how to make gnuplot do it for a very large number of data point (x). Please help

Because I did not know how to make a line like that with many x values in gnuplot, I just found 2 points by solving for two specifc x's...this did work but once I graphed the line I could not figure out how to extend the line further than those two points...

~So if it is possible to extend the line of thosetwo points then what is the code? ... would doing a best fit line for those two points give me the line for all of those data points? If so...how do I do that?

~If not, then what is the code to just graph all of those data points for x?

Any suggestions are appreciated.

Thanks