A coefficient in front of the x will stretch the graph to make it wider or narrower.
A larger coefficient will make the graph narrower, and a smaller coefficient will make the graph wider.
This is because a larger coefficient results in a larger y value, for example coefficient of 1 in front of x^2 will make coordinate (1,1) but a coefficient of 2 in front of x^2 will make the coordinate (1, 2). As you can see a higher coefficient makes the graph higher, and therefore more narrow.
From widest to narrowest, it would be
y = (1/3)x^2,
y = (-3/5)x^2,
y = (8/3)x^2,
because 1/3 < 3/5 < 8/3
