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Which pair of angles are vertical angles? ∠1 and ∠4 ∠1 and ∠2 ∠2 and ∠4 ∠2 and ∠3

Solve the system of equations using the substitution method. {y=−3x+7x=−2y−16 enter your answers in the boxes.

Asource of laser light sends rays ab and ac toward two opposite walls of a hall. the light rays strike the walls at points b and c, as shown below: what is the distance between the walls?