What is the answer to this ??

What is the missing reason in step 5? linear pair postulategivendefinition of complementary anglescongruent complements theorem

Follow these steps using the algebra tiles to solve the equation −5x + (−2) = −2x + 4. 1. add 5 positive x-tiles to both sides and create zero pairs. 2. add 4 negative unit tiles to both sides and create zero pairs. 3. divide the unit tiles evenly among the x-tiles. x =

Atriangle has a side lengths of 18cm, 80 cm and 81cm. classify it as acute obtuse or right?