A landscaping company counted 51 invoices for tree services at the end of the month. They charge $375 for a tree installation and $54 for tree trimming. The total dollar amount of the invoices was $6,606. Let x represent the number of installations and y represent the number of trimmings. Write the ordered pair, (x, y), that represents the situation.

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?