To reset the TI-85 factory settings you would have to use the following keystrokes:
F3 is used to indicate that you want to reset. F1 is to choose everything and F4 is to choose yes for the prompt which asks if you actually want to reset everything.
This would clear all stored data, functions, programs and any custom settings you may have made. The configuration of the calculator is now as it was when you bought it.
To graph the equation of a line like y = 2/3x + 6
First press GRAPH. Next press F1 to select <y(x) =>. Then you enter the equation you want to graph. You would have to use the keystrokes (, 2, divide, 3, ), divide, x-VAR, +, 6
Once the equation is entered, you could entering a RANGE for the x and y values that have to be traced or try out the ZOOM and the TRACE options to view your graph with more clarity