(2x+3)(x-4)-(x+2)(x+3)=x^2+13
2x^2-5x-12-(x^2+5x+6)=x^2+13
2x^2-5x-12-x^2-5x-6=x^2+13
x^2-10x-18=x^2+13
-10x-18=13
10x=-31
x=-31/10＋12