A net is basically a hollow paper 3D figure that was unfolded. So, imagine (or maybe actually do this!) folding both rectangles and the triangle up, so that they almost stand up; move the longest rectangle until it connects with the slanted sides of the triangle. What shape do you get? A triangular prism!
Now, the surface area is the area of each and every one of those shapes, added together. Let's start with the rectangles, left to right, whose area is equal to their length times their width (l*w). For the far left rectangle, 3 cm * 4 cm = 12 sq cm. (Sq stands for square, because you multiply cm by cm, and a short way of saying that is cm squared.) Now, because this is a rectangle, the side opposite the 3cm side is also 3 cm. For the middle rectangle: 3 cm * 3 cm = 9 sq cm.
Again, the right side of the rectangle is also 3 cm, because it's across from another side that measures 3 cm. 3 cm * 5 cm = 15 sq cm. Now, let's move on to the bottom triangle. The area of a triangle is one-half times the base times the height. The base is 3 cm, and the height is 4 cm. 1/2 * 3 cm * 4 cm = 1/2 * 12 sq cm = 6 sq cm. The top triangle is exactly the same as (AKA congruent to) the bottom one, so it's also 6 sq cm. Let's add up the areas of these faces: 12+9+15+6+6=48 sq cm. This is the surface area!
Answer: triangular prism; 48 sq cm
