Question

$frac{3}{x} + frac{21}{ x^{2} -7x} - frac{4-x}{x-7}$

Answer 1

$frac{3(x-7)}{x(x-7)}+ frac{21}{x(x-7)} - frac{(4-x)x}{x(x-7)}= frac{3x-21+21-4x+ x^{2} }{x(x-7)}= frac{ x^{2} -x}{x(x-7)}= = frac{x(x-1)}{x(x-7)}= frac{x-1}{x-7}$