What value can i put for x on 4(x+3) = 4x+3

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

Three baby penguins and their father were sitting on an iceberg 0.50.50, point, 5 meters above the surface of the water. the father dove down 4.74.74, point, 7 meters from the iceberg into the water to catch dinner for his kids. what is the father penguin's position relative to the surface of the water?

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