Let's analyze the given quadrilateral so that we can find m ∠ HEF + m ∠ EFG.
By the definition of a rectangle, we know that EFGH has four right angles. Therefore, the measure of both ∠ HEF and ∠ EFG is 90.
m ∠ HEF + m ∠ EFG = 90 + 90
⇕
m ∠ HEF + m ∠ EFG = 180
