All angles are congruent so just set both equations equal to each other (6x+45=9x+15) to solve that do: -9x on both sides, you get -3x+45=15 and subtract 45, you get -3x=-30, divide by -3 to both sides and you get x=10, another way to prove it would be 6*10=60+45=105 and 9*10=90+15=105. sorry if that wasn’t your question, not sure what a paragraph proof is lol, but that was proving that x=10, hope it helps.