Gifted Issues Discussion homepage Forums Learning Environments What grade level is this math problem?

CCSS puts it at 6th grade. Specifically:

CCSS.Math.Content.6.G.A.1
Find the area of right triangles, other triangles, special quadrilaterals, and polygons by composing into rectangles or decomposing into triangles and other shapes; apply these techniques in the context of solving real-world and mathematical problems.