Start with this t-table:

 x | y
-------
   | 0
   |
   |

First find the x-intercepts by substituting 0 for y












This give us two points with y=0

 x | y
-------
 0 | 0
16 | 0
   |

Now choose a value of x halfway between
the two x-intercepts:

 x | y
-------
 0 | 0
16 | 0
 8 |






So we have this t-table:

 x |  y
--------
 0 |  0
16 |  0
 8 | 64

Use a large scale to accommodate those points.
It is not necessary to mark off the x-axis and 
y-axis with the same scale.

Plot those three points:



Draw an upside-down U-shaped curve through those two points:



Edwin