Answer:
9600 square inches.
Explanation:
We have been given that a puzzle contains a triangular piece with a base of 3 in. and a height of 4 in.
The would used for each triangular piece would be equal to area of triangle.

Each puzzle contains 20 triangular pieces, so wood used for each piece of puzzle would be 20 times 6 square inches.




Therefore, 9600 square inches of wood is needed to make 80 puzzles.