FAN AND MEDAL PLS
Triangle ABC is congruent to triangle DEF. In triangle ABC, side AB measures 13, side BC measures x+13, and side CA measures 16. In triangle DEF, side DE measures 13, side EF measures 3x−20, and side FD measures 16. What equation would help you to solve for the side length of BC and EF? Explain your reasoning using complete sentences.

Question

FAN AND MEDAL PLS 
Triangle ABC is congruent to triangle DEF. In triangle ABC, side AB measures 13, side BC measures x+13, and side CA measures 16. In triangle DEF, side DE measures 13, side EF measures 3x−20, and side FD measures 16. What equation would help you to solve for the side length of BC and EF? Explain your reasoning using complete sentences.

anonymous · Answer

@jim_thompson5910 @dan815 @confluxepic @Loser66 @TheSmartOne @Whitemonsterbunny17 @eliassaab @bibby @EclipsedStar @sleepyjess @bohotness

anonymous · Answer

x+13 = 3x-20 is the equation, I just need help on explaining the reasoning using complete sentences.

anonymous · Answer

well heres what your triangles will look like, just to give you an idea |dw:1426632503187:dw|

anonymous · Answer

I got that, thank you. can you just help me with the rest

anonymous · Answer

@kittenlover731

anonymous · Answer

Reorder the terms: Note: you can or can not do this if you want
13 + x = -20 + 3x

anonymous · Answer

subtract 13 from both sides
13 + x -13= -20 + 3x -13

anonymous · Answer

oh wait im confused here, here use this http://www.algebrahelp.com/calculators/equation/calc.do;jsessionid=25ECE637A1850D7AB7C5834C91ABF374?equation=x%2B13+%3D+3x-20+&solvf=AUTO

anonymous · Answer

That doesnt answer the second question, that just simplify it.

anonymous · Answer

@YinYangInsane