Answer:
B
Explanation:
the surface area is the sum of all individual side areas.
a prism (like a cube that is a special prism) has 6 sides.
top-bottom
left-right
front-back
in our case top and bottom are 5×5 squares.
and the other 4 sides are equal 5×20 rectangles.
so, we get
top-bottom : 2× 5×5 = 50 cm²
left-right : 2× 20×5 = 200 cm²
front-back : 2× 20×5 = 200 cm²
in total we have
200 + 200 + 50 = 450 cm²