3x／（4x+1）- 2x／（5x-3）
=3x(5x-3)/(4x+1)(5x-3)-2x(4x+1)/(4x+1)(5x-3)
=(15x^2-9x-8x^2-2x)/(20x^2-7x-3)
=(7x^2-11x)/(20x^2-7x-3)