$\frac{30}{90}\left(21\right)$

$\frac{d^2}{dx^2}\left(6x^3-10x^2+x\right)$

$\frac{2x^3\:-\:5x^2\:+\:3x\:+\:2}{x^2\:+\:2x\:+\:1}$

$\frac{d}{dx}\left(\frac{e^{x+1}x-2e^{x+1}}{\left(x-1\right)^2}\right)$

$\left(6-8\right)^2-5$

$16x^2-225y^2$