Answer:
376 square centimeters
Step-by-step explanation:
When doubled, the new length is 5*2=10 cm, new width is 4*2=8 cm, and new height is 3*2=6 cm.
The surface area of a rectangular prism is given by : 
Where l is length, w is width, and h is height
Plugging in the new values we get:

The surface area of the enlarged prism = 376 cm^2
The first package is 4 oz (1/4lb) at 79cents = 19.75 cents/oz
Second Package is 8 oz at 1.59 = 19.875 cents / oz
So the first package is cheaper per ounce.
39/100 is the simplest form