You can use a grid to draw a line starting at a specific X and Y distance from a known position.
Choose the Grid Options command 
.
In the Grid Options dialog box, do all of the following:
Set the Show Grid option.
Set the Show Readouts option.
Use the Reposition Origin command 
to specify an origin point on the element whose position you want to reference as you draw the line.
To learn how, see the Help topic, Reposition the grid origin point.
Choose the Line command.
Move the cursor around the sheet or window.
The X and Y coordinates relative to the origin point are displayed adjacent to the cursor.
Click when the cursor is positioned where you want the line to begin.
Click where you want the second point of the line to be, or type the length or angle on the Line command bar and then click to draw the line.
Tip:
To draw lines that snap to the grid intersections, set the Snap To Grid option on the Grid Options dialog box, and then select the Using Points option.
To draw lines that snap to the grid lines, set the Snap To Grid option on the Grid Options dialog box, and then select the Using Lines option.
You can use the Zero Origin command instead of the Reposition Origin command if you want to reference the origin of the drawing sheet, reference plane, or sketch plane.