Question

draw a line through the origin that has a slope of negative 4/3

Answer 1

The origin is just (0,0) and we can multiply that slope, -4/3 by any number to get the second point. let's use x=3 to make is simple as possible,  the second point is then just (3,-4)

Connect (0,0) to (3,-4) and you have your line :)