Heather is building a ladder for her tree house. She will need 13 feet of lumber for each stilt and 2 feet of lumber for each rung on the ladder. How many feet of lumber does she need for a ladder with 2 stilts and 12 rungs?
29 feet because 2 + 13 + 12 + 2 = 29
50 feet because 2 (13) + 12 (2) = 50
160 feet because 13 (12) + 2 (2) = 160
210 feet because (2 + 13) (12 + 2) = 210

Statements reasons 1. ab ? cd; ad ? bc 1. given 2. ac ? ac 2. reflexive property 3. ? adc ? ? cba 3. ? 4. ? dac ? ? bca; ? acd ? ? cab 4. cpctc 5. ? dac and ? bca are alt. int. ? s; ? acd and ? cab are alt. int. ? s 5. definition of alternate interior angles 6. ab ? cd; ad ? bc 6. converse of the alternate interior angles theorem 7. abcd is a parallelogram 7. definition of parallelogram what is the missing reason in step 3?