A plane traveling from Phoenix to Washington, D. C with a tailwind of 20 miles per hour takes 3 hours. The return trip in the same wind, which is now a headwind, takes the same plane 3 hours and 12 minutes. What is the average speed of the plane in calm conditions? 700 miles/hour
600 miles/hour
650 miles/hour
620 miles/hour

Given: lines a and b are parallel and line c is a transversal. prove: 2 is supplementary to 8 what is the missing reason in the proof? statement reason 1. a || b, is a transv 1. given 2. ∠6 ≅ ∠2 2. ? 3. m∠6 = m∠2 3. def. of congruent 4. ∠6 is supp. to ∠8 4. def. of linear pair 5. ∠2 is supp. to ∠8 5. congruent supplements theorem corresponding angles theorem alternate interior angles theorem vertical angles theorem alternate exterior angles theorem