You probably meant:Â "utilize as much of the space AS POSSIBLE on the paper."
Set up and solve an equation of ratios:
 3   8.5
---- = -------
 5    x
Then 3x = 42.5. The image on the paper would be 8.5 by 42.5/3 inches, or 8.5 by 14.17 inches. Won't fit!!
So, try this instead:
 3    x
---- = -------
 5    11
Then 5x =33, and x = 6.6. An image with the same proportions as the 3x5 card will be 6.6 by 11 inches on the 8.5 by 11 inch paper.