use a table of values (it depends how big the graph is)
y = 4x - 9 (list all x values on graph and subsitute to work out y values
x: -1 0 1 2 3
y: -4-9 4(0)-9 4-9 8-9 12-9
=-13 =-9 =-5 =-1 = 3
and so on....
then plot the points on ur graph and join them up. make sure your line crosses the y axis at -9
