Problem
Both bottom cells are shaded in the lower-left triangle, the slant running top-left to bottom-right.
A fourth grader can name the corners of a triangle and see that the slanted edge (hypotenuse) runs from upper-left to lower-right.
4.G.A.1Draw A DiagramA vertical fold turns a lower-left triangle into a lower-right one, so the bottom row cannot match.
Folding left onto right flips the slant; since both bottom slants point the same way, the left-right fold cannot line them up.
4.G.A.3Guess And CheckFold along the horizontal middle instead, sending each bottom tile straight up into an empty cell.
Line symmetry means one half folds onto the other; the cleanest fold here turns the bottom row into the top row.
4.G.A.3Create A Physical RepresentationThe figure can be made symmetric about the horizontal middle line, but not about the vertical one.
A fold line works only if every tile comes to rest on a tile of the very same shape and shading, and folding never alters a shape.
The vertical fold would send the bottom-left tile onto a shape the bottom-right tile does not have, while the horizontal fold sends each bottom tile up into a cell that is still empty and free to match it.
Each cell across the fold is matched with exactly one cell, so the fold succeeds only if every one of those pairs agrees.
Flipping a lower-left triangle over a horizontal crease gives an upper-left triangle.
Flipping a downward triangle over a horizontal crease makes it point upward; doing this to both bottom tiles fills the top row symmetrically.
4.G.A.3Draw A DiagramFolded along that middle line, the top shading lands exactly on the bottom shading.
If the two halves cover each other perfectly when folded, the crease is a real line of symmetry.
4.G.A.3Create A Physical RepresentationFold the paper in half: whatever you draw on top should land right on the matching shape underneath.