a new car worth 21000 is depreciating in value by 3000 per year. after how many years will the cars value be 9000

Which of the following is the best first step in solving the equation below? 4+2㏒³x=17

Given: ae ≅ ce ; de ≅ be prove: abcd is a parallelogram. we have that ab || dc. by a similar argument used to prove that △aeb ≅ △ced, we can show that △ ≅ △ceb by. so, ∠cad ≅ ∠ by cpctc. therefore, ad || bc by the converse of the theorem. since both pair of opposite sides are parallel, quadrilateral abcd is a parallelogram.

What is the answer to this problem? ignore the work. what is the correct answer?