Answer:
500 cm²
Step-by-step explanation:
You haven't presented any diagrams, so I assume the prism has the dimensions shown below.
Then the dimensions of the original piece of cardboard are as in the second figure.
The area of the cardboard is the same as the lateral area of the triangular prism.
The formula for the area of a rectangle is
A = lw
l = 9 cm + 9 cm + 7 cm = 25 cm
w = 20 cm
A = 25 cm × 20 cm = 500 cm²
The area of the piece of cardboard is 500 cm².
