Kelly had to multiply 5, 173, and 20. instead of multiplying the result of 5 of 173 by 20, she recognized that it would be easier to multiply 5 times 20 to get 100, and then multiply 100 times 173 to get 17,300. what property did kelly apply please help its for algebra 1 and 2 and i have no clue ​

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