The surface area would be 768 cm².
Area is a square measurement; therefore to find the ratio of the areas, we square the ratio of the linear measurements:
(5/8)²=5²/8²=25/64
Now we set up a proportion to solve for the missing surface area:
25/64 = 300/x
Cross multiply:
25*x = 300*64
25x = 19200
Divide by 25:
25x/25 = 19200/25
x = 768